TLS KeyUpdate DoS in Go crypto/tls before 1.27.0-rc.3
CVE-2026-56862 Published on August 13, 2026
Limit handshake messages we are willing to accept post-handshake in crypto/tls
Handshake messages, such as KeyUpdate, are always considered as state-advancing, regardless of whether a handshake has been completed or not. As a result, a malicious client can keep sending KeyUpdate messages to force the server to keep performing key derivation operations indefinitely.
Affected Versions
Go standard library crypto/tls:- Before 1.25.13 is affected.
- Version 1.26.0-0 and below 1.26.6 is affected.
- Version 1.27.0-0 and below 1.27.0-rc.3 is affected.