Vulnerability Note VU#940388

Overview

Gnu Privacy Guard (GnuPG) is a cryptographic utility used to generate cryptographic keys and perform other cryptographic functions. A vulnerability in the way GnuPG generates ElGamal keys has been discovered. This vulnerability renders ElGamal signing key untrustworthy.

Description

A vulnerability in the algorithm to generate ElGamal sign+encrypt keys can permit an attacker to generate valid signatures without access to the private key. This vulnerability does not affect encrypt-only (type 16) ElGamal keys, only the ElGamal sign+encrypt key (type 20) when used to make a signature with a GnuPG version 1.0.2 or later.

Impact

A remote attacker can generate a valid signature without access to the private key.

Solution

Revoke your ElGamal signing keys. GnuPG has released a patch for version 1.2.3 or you can upgrade to version 1.2.4 or later.

Systems Affected (Learn More)

Vendor	Status	Date Notified	Date Updated
GNU Privacy Guard	Affected	-	29 Dec 2003

If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group	Score	Vector
Base	N/A	N/A
Temporal	N/A	N/A
Environmental	N/A	N/A

References

• http://www.secunia.com/advisories/10304/
• http://www.securityfocus.com/bid/9115
• http://www.secunia.com/advisories/10349/
• http://www.secunia.com/advisories/10400/
• http://www.secunia.com/advisories/10399/

Credit

Thanks to Werner Koch for his advisory on this issue, and Phong Nguyen for reporting this vulnerability.

This document was written by Jason A Rafail.

Other Information

• CVE IDs: CAN-2003-0971
• Date Public: 27 Nov 2003
• Date First Published: 29 Dec 2003
• Date Last Updated: 29 Dec 2003
• Severity Metric: 6.33
• Document Revision: 7