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Ethereal integer underflow when parsing malformed PGM packets with NAK lists

Vulnerability Note VU#433596

Original Release Date: 2004-03-24 | Last Revised: 2004-03-25


Ethereal fails to properly parse Pragmatic General Multicast (PGM) packets containing a crafted negative acknowledgement (NAK) list.


Ethereal is a network traffic analysis package. It includes the ability to decode packets containing PGM data. There is a vulnerability in the way the PGM protocol dissector parses PGM data containing a crafted NAK list.

According to the e-matters Security Advisory:

"When parsing an PGM packet with a carefully crafted NakList a possible integer underflow can result in a very small stack-overflow. Due to the stacklayout code execution exploitation seems very unlikely."


A remote, unauthenticated attacker could cause Ethereal to crash or possibly execute arbitrary code on the vulnerable system.



Upgrade to version 0.10.3 or later.

Note: Ethereal is considered BETA software at this time.

Disable Dissector

If you are unable to upgrade to version 0.10.3 or later, you can disable the PGM protocol dissector by performing the following actions in Ethereal:

(for Ethereal versions 0.8.x and 0.9.x)
1) Select Edit->Protocols
2) Deselect the PGM protocol dissector from the list

(for Ethereal versions 0.10.x)
1) Select Analyze->Enabled Protocols
2) Disable the PGM protocol dissector from the list by unchecking its "Status" checkbox

Vendor Information


Ethereal Affected

Updated:  March 24, 2004



Vendor Statement

Please see the Ethereal Security Bulletin at

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

CVSS Metrics

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Ethereal credits Stefan Esser for reporting this vulnerability.

This document was written by Damon Morda.

Other Information

CVE IDs: CVE-2004-0176
Severity Metric: 4.04
Date Public: 2004-03-22
Date First Published: 2004-03-24
Date Last Updated: 2004-03-25 15:34 UTC
Document Revision: 22

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