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OpenSSL TLS 1.3 server may choose unexpected key agreement group

OpenSSL · CVE-2026-2673
0 news outlets0 CERTs and agencies0 researchers

Assessment: Track

SSVC decision points: exploitation none, automatable yes, technical impact partial, deployment high.

What is it?

Issue summary: An OpenSSL TLS 1.3 server may fail to negotiate the expected preferred key exchange group when its key exchange group configuration includes the default by using the 'DEFAULT' keyword. Impact summary: A less preferred key exchange may be used even when a more preferred group is supported by both client and server, if the group was not included among the client's initial predicated keyshares. This will sometimes be the case with the new hybrid post-quantum groups, if the client chooses to defer their use until specifically requested by the server. If an OpenSSL TLS 1.3 server's configuration uses the 'DEFAULT' keyword to interpolate the built-in default group list into its own configuration, perhaps adding or removing specific elements, then an implementation defect causes the 'DEFAULT' list to lose its 'tuple' structure, and all server-supported groups were treated as a single sufficiently secure 'tuple', with the server not sending a Hello Retry Request (HRR) even when a group in a more preferred tuple was mutually supported. As a result, the client and server might fail to negotiate a mutually supported post-quantum key agreement group, such as 'X25519MLKEM768',

Evidence

No coverage recorded yet.

Exploitation

  • Public proof of concept
  • Exploited in the wild
  • Listed as known exploited
CVSS
6.5
EPSS
0.5%
First seen
12 h ago
Status
corroborated

All OpenSSL vulnerabilities