Common Desktop Environment 2.3.1 Buffer Overflow

@Mediaservice.net Security Advisory #2020-02 (last updated on 2020-01-15)

         Title:Local privilege escalation via CDE dtsession
   Application: Common Desktop Environment 2.3.1 and earlier
Common Desktop Environment 1.6 and earlier
     Platforms:Oracle Solaris 10 1/13 (Update 11) and earlier
Other platforms are potentially affected (see below)
   Description:A local attacker can gain root privileges by exploiting a
buffer overflow in CDE dtsession
        Author:Marco Ivaldi <[email protected]>
 Vendor Status:Oracle <[email protected]> notified on 2019-11-13
CERT/CC notified on 2019-12-09 (tracking VU#308289)
      CVE Name:CVE-2020-2696
   CVSS Vector:CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H (Base Score: 8.8)
    References: https://github.com/0xdea/advisories/blob/master/2020-02-cde-dtsession.txt
https://www.oracle.com/security-alerts/cpujan2020.html
https://sourceforge.net/p/cdesktopenv/wiki/Home/
https://www.oracle.com/technetwork/server-storage/solaris10/
https://www.mediaservice.net/
https://0xdeadbeef.info/

1. Abstract

A buffer overflow in the CheckMonitor() function in the Common Desktop
Environment 2.3.1 and earlier and 1.6 and earlier, as distributed with Oracle
Solaris 10 1/13 (Update 11) and earlier, allows local users to gain root
privileges via a long palette name passed to dtsession in a malicious
.Xdefaults file.

Note that Oracle Solaris CDE is based on the original CDE 1.x train, which is
different from the CDE 2.x codebase that was later open sourced. Most notably,
the vulnerable buffer in the Oracle Solaris CDE is stack-based, while in the
open source version it is heap-based.

2. Example Attack Session.

bash-3.2$ cat /etc/release
                    Oracle Solaris 10 1/13 s10x_u11wos_24a X86
  Copyright (c) 1983, 2013, Oracle and/or its affiliates. All rights reserved.
                            Assembled 17 January 2013
bash-3.2$ uname -a
SunOS nostalgia 5.10 Generic_147148-26 i86pc i386 i86pc
bash-3.2$ id
uid=54322(raptor) gid=1(other)
bash-3.2$ gcc raptor_dtsession_ipa.c -o raptor_dtsession_ipa -Wall
bash-3.2$ ./raptor_dtsession_ipa 192.168.1.1:0
raptor_dtsession_ipa.c - CDE dtsession LPE for Solaris/Intel
Copyright (c) 2019-2020 Marco Ivaldi <[email protected]>

Using SI_PLATFORM       : i86pc (5.10)
Using stack base        : 0x8047fff
Using rwx_mem address   : 0xfeffa004
Using payload address   : 0x8047dff
Using strcpy() address  : 0xfefe26a0

# id
uid=0(root) gid=1(other)

3. Affected Platforms.

All platforms shipping the Common Desktop Environment are potentially affected.
This includes:

* Oracle Solaris 10 1/13 (Update 11) and earlier [default installation]

According to the CDE Wiki, the following platforms are officially supported:

* All Official Ubuntu variants 12.04 - 18.04
* Debian 6, 7, 8, 9
* Fedora 17 at least
* Archlinux
* Red Hat
* Slackware 14.0
* OpenBSD
* NetBSD
* FreeBSD 9.2, 10.x, 11.x
* openSUSE Tumbleweed (gcc7)
* openSUSE Leap 4.2 (gcc4)
* SUSE 12 SP3 (gcc4)
* Solaris, OpenIndiana

4. Fix.

The maintainers of the open source CDE 2.x version have issued the following
patches for this vulnerability:
https://sourceforge.net/p/cdesktopenv/mailman/message/36900154/
https://sourceforge.net/p/cdesktopenv/code/ci/6b32246d06ab16fd7897dc344db69d0957f3ae08/

Oracle, which maintains a different CDE codebase based on the 1.x train, has
assigned the tracking# S1231688 and has released a fix for all affected and
supported versions of Solaris in their Critical Patch Update (CPU) of January
2020.

As a workaround, it is also possible to remove the setuid bit from the
vulnerable executable as follows (note that this might prevent it from working
properly):

bash-3.2# chmod -s /usr/dt/bin/dtsession

Please note that during the audit many other potentially exploitable bugs have
surfaced in dtsession and in the Common Desktop Environment in general.
Therefore, removing the setuid bit from all CDE binaries is recommended,
regardless of patches released by vendors.

5. Proof of Concept.

An exploit for Oracle Solaris 10 1/13 (Update 11) Intel has been developed as a
proof of concept. It can be downloaded from:

https://github.com/0xdea/exploits/blob/master/solaris/raptor_dtsession_ipa.c

Copyright (c) 2020 Marco Ivaldi and @Mediaservice.net. All rights reserved.

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