CVE-2026-42505

Handshakes which used Encrypted Client Hello could be de-anonymized by a passive network observer due to a disclosure of pre-shared key identities in the unencrypted client hello.

• golang-1.27 1.27~rc2-1
• golang-1.26 1.26.5-1
• golang-1.25 1.25.12-1
• golang-1.24 [trixie] - golang-1.24 (Minor issue)
• golang-1.19 [bookworm] - golang-1.19 (crypto/tls client ECH introduced in Go 1.23; absent in 1.19)
• golang-1.15 (Vulnerable code introduced later) crypto/tls client Encrypted Client Hello introduced in Go 1.23 (issue #63369) https://groups.google.com/g/golang-announce/c/OrmQE_Yp5Sc https://github.com/golang/go/issues/79282 Fixed by: https://github.com/golang/go/commit/ca8ca590ccfda1e1c3186faf975afdb02cb6d2f0 (go1.26.5) Fixed by: https://github.com/golang/go/commit/fc9f821bb660c1dcb9e57868b62f62bf3afb5842 (go1.25.12)