CVE-2026-56865
GOPROXY can serve forged sumdb tiles to bypass Go module verification.
Is CVE-2026-56865 being exploited?
Not confirmed. CVE-2026-56865 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.11% probability of exploitation in the next 30 days.
How severe is CVE-2026-56865?
CVE-2026-56865 is rated High with a CVSS score of 8.4. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-56865?
Yes. A fix has been recorded for CVE-2026-56865. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-56865 affect?
CVE-2026-56865 affects Go toolchain (go command), GOPROXY implementations, Go module cache, CI/CD build systems using Go modules. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-56865?
Update Go to patched release; clear module cache and run: rm -r go.sum go.work.sum vendor/ && go mod tidy
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Malicious GOPROXY can bypass go.sum/sumdb checks, persist attacker-controlled modules to local cache, enabling supply-chain code injection and potential RCE during builds.
Immediate action required
- affected< 1.25.13
- affected>= 1.26.0-0 and < 1.26.6
- affected>= 1.27.0-0 and < 1.27.0-rc.3
- affected< 0.40.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.