Vulnerability in Go's TLS Implementation Affects Encrypted Client Hello Communication
CVE-2026-42505

5.3MEDIUM

Key Information:

Vendor

Go Standard Library

Status
Crypto/tls
Vendor
CVE Published:
8 July 2026

What is CVE-2026-42505?

A vulnerability exists in the TLS implementation of Go, where handshakes utilizing Encrypted Client Hello can be de-anonymized by passive network observers. This occurs due to the exposure of pre-shared key identities within the unencrypted Client Hello message, potentially compromising user privacy and enabling targeted attacks. Effective mitigation strategies should be employed to protect users from this vulnerability in their communications.

Affected Version(s)

crypto/tls 0 < 1.25.12

crypto/tls 1.26.0-0 < 1.26.5

crypto/tls 1.27.0-0 < 1.27.0-rc.2

References

https://go.dev/cl/775960
https://go.dev/issue/79282
https://groups.google.com/g/golang-announce/c/OrmQE_Yp5Sc

CVSS V3.1

Score:
5.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Coia Prant (github.com/rbqvq)
.