What’s Vulnerable › Vulnerabilities

CVE-2026-42505: Invoking Encrypted Client Hello privacy leak in crypto/tls

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-201

Description

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.

Affected products

• Go: from 1.23.0 before 1.25.12; from 1.26.0 before 1.26.5; 1.27-rc1 — fixed in 1.25.12, 1.26.5
• Go Stdlib: before 1.25.12; from 1.26.0-0 before 1.26.5; from 1.27.0-0 before 1.27.0-rc.2 — fixed in 1.25.12, 1.26.5, 1.27.0-rc.2

How to fix

Upgrade to a fixed version: Go 1.25.12, 1.26.5; Go Stdlib 1.25.12, 1.26.5, 1.27.0-rc.2. Check the vendor advisory for mitigations.

References

• https://go.dev/cl/775960
• https://go.dev/issue/79282
• https://groups.google.com/g/golang-announce/c/OrmQE_Yp5Sc
• https://pkg.go.dev/vuln/GO-2026-5856

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