CVE-2026-56864: Ignore unrelated, unauthenticated hashes in Lookup in golang.org/x/mod/sumdb

CSIRTS triage

What

The sumdb Lookup function ignores unauthenticated hashes from unrelated sources, bypassing integrity verification.

Who is affected

All Go module users relying on sumdb for dependency verification.

Urgency

High priority; CVSS 7.5 indicates authentication bypass in dependency security.

Action

Update golang.org/x/mod to the patched version addressing CVE-2026-56864.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source

Microsoft Security Response Center (INTL · vendor-psirt · site)

Severity

high — CVSS 7.5

Published

2026-08-11

Exploitation

Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56864

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

• Low exploitation riskCVE-2026-568640.25% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 16% of all EPSS-scored CVEs.

Referenced CVEs

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

• high[NEW] [high] Golang Go: Multiple vulnerabilitiescert-bund
• highCVE-2026-56864: A malicious GOSUMDB was capable of serving arbitrary module content not contained within the t…nvd

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