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
Products Associated with CVE-2026-56864
Want to know whenever a new CVE is published for GoLang Go? stack.watch will email you.
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.