CyberSecBulletin
CVE-2026-56865NVD status: Awaiting Analysis

cmd/go: Improper Verification of Cryptographic Signature

Published Updated By the CyberSecBulletin desk

CVE-2026-56865 is a high-severity improper verification of cryptographic signature vulnerability in cmd/go from Go toolchain, with a CVSS 3.1 base score of 8.4 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, without any action from a user. The record lists versions 1.25.13, 1.26.6, 1.27.0-rc.3 as the first without the flaw, so updating cmd/go to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.13% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update cmd/go to 1.25.13 or 1.26.6 or 1.27.0-rc.3, whichever matches your release line, or a later version.
  2. Update golang.org/x/mod/sumdb/tlog to 0.40.0 or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
Go toolchaincmd/gobefore 1.25.13; 1.26.0-0 up to, but not including, 1.26.6; 1.27.0-0 up to, but not including, 1.27.0-rc.31.25.13, 1.26.6, 1.27.0-rc.3
Golang.org/x/modgolang.org/x/mod/sumdb/tlogbefore 0.40.00.40.0

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).

Official description

A malicious GOPROXY was previously capable of forging up to two sumdb tiles that allow for a requested module to bypass the GOSUMDB check and persist attacker-controlled module content to a local Go module cache. This attack allows for a malicious GOPROXY to serve malicious module content that cannot be detected by evaluating the transparency log. All tiles are now correctly verified against their parents. In order to determine if you have been affected: rm -r go.sum go.work.sum vendor/ && go mod tidy

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Verification of Cryptographic Signature

The product does not verify, or incorrectly verifies, the cryptographic signature for data.

More Improper Verification of Cryptographic Signature vulnerabilities (CWE-347)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in cmd/go

All cmd/go vulnerabilities

Recent Improper Verification of Cryptographic Signature vulnerabilities

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