---
id: CVE-2026-42505
title: >-
  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.
summary: >-
  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.
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N'
cwe:
  - CWE-201
vendor: golang
product: go
affected:
  - 'go >= 1.23.0, < 1.25.12'
  - 'go >= 1.26.0, < 1.26.5'
  - go = 1.27
patched:
  - go 1.26.5
published: '2026-07-08'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T20:14:44.473'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-42505'
references:
  - url: 'https://go.dev/cl/775960'
    label: security@golang.org
  - url: 'https://go.dev/issue/79282'
    label: security@golang.org
  - url: 'https://groups.google.com/g/golang-announce/c/OrmQE_Yp5Sc'
    label: security@golang.org
  - url: 'https://pkg.go.dev/vuln/GO-2026-5856'
    label: security@golang.org
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42505.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-42505'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2498138'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-42505'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-42505'
  - url: 'https://access.redhat.com/errata/RHSA-2026:37436'
  - url: 'https://access.redhat.com/errata/RHSA-2026:38995'
  - url: 'https://access.redhat.com/errata/RHSA-2026:37435'
  - url: 'https://access.redhat.com/errata/RHSA-2026:36510'
  - url: 'https://access.redhat.com/errata/RHSA-2026:36477'
  - url: 'https://access.redhat.com/errata/RHSA-2026:54773'
tags:
  - nvd
  - csaf
  - vex
  - red-hat
  - osv
  - go
epss: 0.00413
epssPercentile: 0.32819
aliases:
  - GO-2026-5856
ecosystem: go
ingestedAt: '2026-07-09T18:56:37.250Z'
---

## Overview

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

- `go >= 1.23.0, < 1.25.12`
- `go >= 1.26.0, < 1.26.5`
- `go = 1.27`

## Remediation

Upgrade past the affected range:

- `go 1.26.5`

## Package advisory (CVE-2026-42505)

Affected packages:

- `stdlib >= 1.27.0-0, < 1.27.0-rc.2`

Patched in:

- `stdlib 1.27.0-rc.2`

Source: https://osv.dev/vulnerability/GO-2026-5856

## Vendor advisories

- **RHSA-2026:37436** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 10) · released 2026-07-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:37436)
- **RHSA-2026:38995** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8) · released 2026-07-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:38995)
- **RHSA-2026:37435** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9) · released 2026-07-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:37435)
- **RHSA-2026:36510** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-07-08 · [advisory](https://access.redhat.com/errata/RHSA-2026:36510)
- **RHSA-2026:36477** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-07-08 · [advisory](https://access.redhat.com/errata/RHSA-2026:36477)
- **RHSA-2026:54773** · Red Hat · fixed in: Red Hat OpenShift distributed tracing 3.10.2 · released 2026-08-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:54773)
- **Red Hat VEX** · Moderate · affected: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift, Compliance Operator, Confidential Compute Attestation, Cryostat 4, … · no fix planned: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift, Compliance Operator, … · updated 2026-09-08 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42505.json)