What is the CVSS score of CVE-2026-42508?

CVE-2026-42508 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.0%.

Which versions of golang.org/x/crypto are affected by CVE-2026-42508?

A certificate revocation validation flaw in the Go SSH cryptography library allows attackers with revoked host keys to impersonate legitimate servers, potentially compromising SSH-based…. A patch is available.

How to fix or mitigate CVE-2026-42508?

Within 24 hours: Identify all applications and services using golang.org/x/crypto and document their current versions. Within 7 days: Update golang.org/x/crypto to version 0.52.0 or later in development and staging environments; test certificate revocation functionality. Within 30 days: Deploy patched version to all production systems; confirm revocation validation is operational.

golang.org/x/crypto CVE-2026-42508

EUVD-2026-31399 CRITICAL

Improper Certificate Validation (CWE-295)

2026-05-22 Go

GHSA-5cgq-3rg8-m6cv

Information Disclosure Golang Org X Crypto Ssh Knownhosts

9.1

CVSS 3.1 · Vendor: Go

Severity by source

Vendor (Go) PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

SUSE

CRITICAL

qualitative

Red Hat

7.4 HIGH

qualitative

Primary rating from Vendor (Go).

CVSS VectorVendor: Go

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

May 28, 2026 - 15:08 vuln.today

CVSS changed

May 28, 2026 - 15:07 NVD

9.1 (None) 9.1 (CRITICAL)

Patch available

May 22, 2026 - 04:31 EUVD

CVE Published

May 22, 2026 - 02:31 nvd

UNKNOWN (no severity yet)

DescriptionCVE.org

Previously, a revoked 'SignatureKey' belonging to a CA was not correctly checked for revocation. Now, both the 'key' and 'key.SignatureKey' are checked for @revoked.

AnalysisAI

Improper certificate revocation validation in the golang.org/x/crypto/ssh/knownhosts package allows SSH connections to succeed against hosts whose CA SignatureKey has been revoked. Versions prior to 0.52.0 only validated the leaf 'key' against revocation entries while ignoring 'key.SignatureKey', enabling attackers holding a revoked CA-signed host key to impersonate trusted servers. No public exploit identified at time of analysis, and EPSS exploitation probability is very low at 0.02%.

Technical ContextAI

The flaw resides in golang.org/x/crypto/ssh/knownhosts, the Go standard ecosystem library used by SSH clients (including those built on golang.org/x/crypto/ssh) to validate remote host keys against a known_hosts file. The library supports @cert-authority entries that delegate trust to a CA which signs host certificates; revocation is expressed via @revoked entries. CWE-295 (Improper Certificate Validation) applies because the revocation check examined only the presented host key without recursively checking the embedded SignatureKey identifying the signing CA, so a revoked CA could still produce host certificates accepted as valid by client applications.

RemediationAI

Vendor-released patch: golang.org/x/crypto v0.52.0. Update the module in go.mod with 'go get golang.org/x/crypto@v0.52.0' and rebuild and redeploy any binaries that consume ssh/knownhosts, since the fix ships compiled into the application rather than as a runtime library. Confirm the upgrade via the Go announcement at https://groups.google.com/g/golang-announce/c/a082jnz-LvI and the advisory at https://pkg.go.dev/vuln/GO-2026-5021. If patching cannot occur immediately, compensating controls include removing @cert-authority entries from known_hosts files and pinning specific host keys directly (trade-off: loses CA-based scalability and requires manual key rotation), or rotating the trusted CA so the previously-revoked key is no longer in the trust chain (trade-off: requires re-signing all host certificates). 'govulncheck' should be run across the codebase to confirm no residual import paths remain on vulnerable versions.