Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')
Weakness ID: 757 (Weakness Class)Status: Incomplete
+ Description

Description Summary

A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.

Extended Description

When a security mechanism can be forced to downgrade to use a less secure algorithm, this can make it easier for attackers to compromise the software by exploiting weaker algorithm. The victim might not be aware that the less secure algorithm is being used. For example, if an attacker can force a communications channel to use cleartext instead of strongly-encrypted data, then the attacker could read the channel by sniffing, instead of going through extra effort of trying to decrypt the data using brute force techniques.

+ Observed Examples
CVE-2006-4302Attacker can select an older version of the software to exploit its vulnerabilities.
CVE-2006-4407Improper prioritization of encryption ciphers during negotiation leads to use of a weaker cipher.
CVE-2005-2969chain: SSL/TLS implementation disables a verification step (CWE-325) that enables a downgrade attack to a weaker protocol.
CVE-2001-1444Telnet protocol implementation allows downgrade to weaker authentication and encryption using a man-in-the-middle attack.
CVE-2002-1646SSH server implementation allows override of configuration setting to use weaker authentication schemes. This may be a composite with CWE-642.
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class693Protection Mechanism Failure
Research Concepts (primary)1000
+ Relationship Notes

This is related to CWE-300 (Man-in-the-Middle), although not all downgrade attacks necessarily require a man in the middle. See examples.

+ Content History
Submission DateSubmitterOrganizationSource
2009-03-03Internal CWE Team