Go Module Auth Bypass via Malicious GOSUMDB (before 1.26.6, 1.27.0-rc.3)
CVE-2026-56864 Published on August 13, 2026
Ignore unrelated, unauthenticated hashes in Lookup in golang.org/x/mod/sumdb
A malicious GOSUMDB was capable of serving arbitrary module content not contained within the transparency log. This attack allows for a coordinating GOPROXY and GOSUMDB to serve a client malicious module content that cannot be detected by evaluating the transparency log. In order to determine if you have been affected: rm -r go.sum go.work.sum vendor/ && go mod tidy
Vulnerability Analysis
CVE-2026-56864 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality, with no impact on integrity and availability.
Weakness Type
Improper Verification of Cryptographic Signature
The software does not verify, or incorrectly verifies, the cryptographic signature for data.
Products Associated with CVE-2026-56864
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Affected Versions
Go toolchain cmd/go:- Before 1.25.13 is affected.
- Version 1.26.0-0 and below 1.26.6 is affected.
- Version 1.27.0-0 and below 1.27.0-rc.3 is affected.
- Before 0.40.0 is affected.