Kerio Personal Firewall Multiple IP Options Denial of Service

Release Date:
November 9, 2004

Date Reported:
October 30, 2004

Severity:
High (Remote Denial of Service)

Vendor:
Kerio

Systems Affected:
Kerio Personal Firewall 4.1.1 and prior

Overview:
eEye Digital Security has discovered a severe denial of service
vulnerability in the Kerio Personal Firewall product for Windows. The
vulnerability allows a remote attacker to reliably render a system
inoperative with one single packet. Physical access is required in order
to bring an affected system out of this "frozen" state. This specific
flaw exists within the component that performs low level processing of
TCP, UDP, and ICMP packets. 

Technical Details:
The vulnerability exists in FWDRV.SYS when trying to parse through the
IP Options in a TCP, UDP, or ICMP packet. When an attacker supplies a
single TCP, UDP, or ICMP packet with an IP Option followed by a length
of 0x00, the FWDRV.SYS driver enters an infinite loop and causes the
operating system to "freeze up" to the point where it can no longer be
accessed outside of the system itself nor can any part of the GUI be
accessed including keyboard and mouse. The only way to bring the system
back online is to hard boot the system which requires physical access of
the system. The attacker only needs to send a single packet to any port
on the system regardless of whether or not the port is open. This flaw
is still accessible even if the firewall is set to "stop all traffic"
because it still continues to process packets. The vulnerable code
maintains an offset into the IP option bytes, and attempts to advance
past a variable-length option by adding its length to the offset. If the
option's length field is zero, then this will result in an infinite loop
and the machine halts completely. It should be noted that since there is
not a state requirement for performing this attack, it is possible to
spoof a TCP, UDP, or ICMP packet. This results in an attacker's ability
to remain anonymous.

For those who pay attention you might have noticed that this
vulnerability is _identical_ to the Symantec vulnerability we released a
few months back.
http://www.eeye.com/html/research/advisories/AD20040423.html This is
important to illustrate as we hope that more software vendors become
more diligent about reading the very important technical details held
within advisories so that they can better secure their code/customers
from already known attacks such as this one.

Protection:
Retina Network Security Scanner has been updated to identify this
vulnerability.

Vendor Status:
Kerio has provided an update to their Personal Firewall 4. Please
download 4.1.2 or later from http://www.kerio.com/kpf_download.html.
Kerio has also released a security advisory at
http://www.kerio.com/security_advisory.html.

Credit:
Discovery: Karl Lynn

Related Links:
Retina Network Security Scanner - Free 15 Day Trial
http://www.eeye.com/html/Products/Retina/download.html

Copyright (c) 1998-2004 eEye Digital Security
Permission is hereby granted for the redistribution of this alert
electronically. It is not to be edited in any way without express
consent of eEye. If you wish to reprint the whole or any part of this
alert in any other medium excluding electronic medium, please email
alert@eEye.com for permission.

Disclaimer
The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There
are no warranties, implied or express, with regard to this information.
In no event shall the author be liable for any direct or indirect
damages whatsoever arising out of or in connection with the use or
spread of this information. Any use of this information is at the user's
own risk.