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November 21, 2005
Symantec Dynamic VPN Services: ISAKMP Denial of Service

Revision History


Remote AccessYes
Local AccessNo
Authentication RequiredNo
Exploit publicly availableNo


The NISCC (National Infrastructure Security Co-ordination Centre) a UK-sponsored inter-departmental agency has identified nearly five-thousand potential ISAKMP vulnerabilities. Test for these vulnerabilities were created by the NISCC and distributed to an unspecified number of vendors including Symantec.

While proactively testing our products against these vulnerabilities, Symantec uncovered a buffer overflow in two out of the five-thousand tests that can lead to a denial of service of the dynamic VPN services.

Affected Product(s)

Symantec Enterprise FirewallWindows8.0SEF8.0-20051114-00
Symantec Gateway Security5000 Series3.0SGS3.0-2005114-02
5100 SG7004-20051114-00
Symantec Firewall /VPN Appliance200/200RAllBuild 1.8F
100AllBuild 1.8F
Symantec Gateway Security4002.0Build 1103
3002.0Build 1103

Not Affected Product(s)

Symantec Clientless VPN Gateway44005.0

Dynamic IPsec VPN tunnels require the use of ISAKMP (Internet Security Association and Key Management Protocol), a standard protocol that provides the framework for establishing, negotiating, modifying, and deleting security associations. The ISAKMP service listens on UDP port 500 on all the affected security gateways. Under certain conditions a malformed ISAKMP packet can potentially cause the ISAKMP service to crash therefore affecting the ability and stability of dynamic VPN tunnels.

Symantec Response
Symantec engineers created patches to correct this issue. The patches listed above are available via the Symantec Enterprise Support site:


Symantec is not aware of any active attempts against or customers impacted by this issue. M

As a part of normal best practices, users should keep vendor-supplied patches for all application software and operating systems up-to-date. Symantec strongly recommends any affected customers update their product immediately to protect against these types of threats.

Symantec takes the security and proper functionality of our products very seriously. As founding members of the Organization for Internet Safety (OISafety), Symantec supports and follows the principles of responsible disclosure. Symantec also subscribes to the vulnerability disclosure guidelines outlined by the National Infrastructure Advisory Council (NIAC).

Please contact secure@symantec.com if you feel you have discovered a security issue in a Symantec product. A Symantec Product Security team member will contact you regarding your submission. Symantec strongly recommends using encrypted email for reporting vulnerability information to secure@symantec.com. The Symantec Product Security PGP key can be found at the end of this message.

Symantec has developed a Product Vulnerability Response document outlining the process we follow in addressing suspected vulnerabilities in our products. This document is available below.

PDF Symantec Vulnerability Response Policy PGP Symantec Product Vulnerability Management PGP Key

Copyright © by Symantec Corp.
Permission to redistribute this alert electronically is granted as long as it is not edited in any way unless authorized by Symantec Security Response. Reprinting the whole or part of this alert in any medium other than electronically requires permission from secure@symantec.com.

The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.

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Initial Post on: Monday, 21-Nov-05 13:35:00
Last modified on: Monday, 21-Nov-2005 13:45:21 PST
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