Symantec Multiple Firewall Remote DNS KERNEL Overflow

Release Date:
May 12, 2004

Date Reported:
April 19, 2004

Severity:
High (Remote Kernel Access)

Vendor:
Symantec

Systems Affected:
Symantec Norton Internet Security 2002
Symantec Norton Internet Security 2003
Symantec Norton Internet Security 2004
Symantec Norton Internet Security Professional 2002
Symantec Norton Internet Security Professional 2003
Symantec Norton Internet Security Professional 2004
Symantec Norton Personal Firewall 2002
Symantec Norton Personal Firewall 2003
Symantec Norton Personal Firewall 2004 
Symantec Client Firewall 5.01, 5.1.1 
Symantec Client Security 1.0, 1.1, 2.0(SCF 7.1)
Symantec Norton AntiSpam 2004

Description:
eEye Digital Security has discovered a critical remote vulnerability
within the Symantec firewall product line. A buffer overflow exists
within a core driver component that handles the processing of DNS
(Domain Name Service) requests and responses. By sending a DNS Resource
Record with an overly long canonical name, a traditional stack-based
buffer overflow is triggered. Successful exploitation of this flaw
yields remote KERNEL access to the system.

With the ability to freely execute code at the Ring 0 privilege level,
there are literally no boundaries for an attacker.

It should also be noted, that due to a separate design flaw in the
firewalls handling of incoming packets, this attack can be successfully
performed with all ports filtered, and all intrusion rules set.

Technical Description:
This specific vulnerability exists within the SYMDNS.SYS driver. The
stack overflow arises due to an implementation flaw in the routine that
processes the CNAME field of incoming Resource Records. A canonical name
field is represented as a series of labels, and is terminated by a label
with a zero byte length. Each string consists of a one byte length
specifier, followed by that number of characters. A typical canonical
name field would be of the following format:

0x03 // length 
www // string component
0x04 // length 
eEye // string component
0x03 // length 
com // string component

Each time the SYMDNS.SYS driver encounters a length field, the field is
then used as a counter to copy the bytes that follow. These bytes are
copied directly into a stack based buffer. Due to poor sanity checking
on the total CNAME field, the routine will accept a large number of
length specifiers and byte sequences. As the routine loops through each
field, the bytes are concatenated, and an exploitable condition in the
KERNEL is reached.

A separate design flaw allows this attack to succeed with the firewall
running at it's most locked-down state. The firewall will happily accept
any packet that has a source port of 53, regardless of port filtering.

The fact that this vulnerability is exploitable over UDP adds another
serious layer to an already critical flaw.

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

Vendor Status:
Symantec has released a patch for this vulnerability. The patch is
available via the Symantec LiveUpdate service. For more information
please refer to the Symantec security advisory.
http://securityresponse.symantec.com/avcenter/security/Content/2004.05.1
2.html 

Credit:
Discovery: Barnaby Jack and Karl Lynn

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

Greetings:
R Hassell (aka Gilligan), the NZ crew, Gary Golomb, Rich Walchuck, Jason
Dameron, Sam Stover, Matt Dickerson, and Kelly H.

Copyright (c) 1998-2004 eEye Digital Security
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