What is CVE-2026-42505?

CVE-2026-42505 is a medium-severity vulnerability in Golang Go, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 5.3/10. Published 2026-07-08.

How severe is CVE-2026-42505?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Golang Go

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.

Published 2026-07-08 · last modified 2026-09-16.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.004 (30.1th percentile), scored 2026-10-09.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 30th percentile — 30.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Golang Go — versions 1.27
Go Standard Library Crypto/tls — versions 0, 1.26.0-0, 1.27.0-0

Weakness classification (CWE)

CWE-201 — Insertion of Sensitive Information into Sent Data

References

go.dev/cl/775960 (Patch)
go.dev/issue/79282 (Patch, Issue Tracking)
groups.google.com/g/golang-announce/c/OrmQE_Yp5Sc (Mailing List, Release Notes, Vendor Advisory)
pkg.go.dev/vuln/GO-2026-5856 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-42505?: CVE-2026-42505 is a medium-severity vulnerability in Golang Go, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 5.3/10. Published 2026-07-08.
How severe is CVE-2026-42505?: Medium severity. CVSS v3 base score is 5.3 out of 10.