Google · Go · CVE-2026-42501
**Name of the Vulnerable Software and Affected Versions**
Go (affected versions not specified)
**Description**
A flaw in the `go` command's validation of module checksums allows a malicious module proxy to bypass checksum database validation. This occurs when the checksum database returns a successful response that contains no entry for the module, leading the `go` command to incorrectly permit validation to succeed. Consequently, a malicious proxy can serve altered versions of the Go toolchain or modules. This is particularly critical when a different toolchain version is selected via the `GOTOOLCHAIN` environment variable, a `go.work` file, or a `go.mod` file, as the `go` command will download and execute the toolchain provided by the proxy. The issue affects users utilizing an untrusted module proxy (`GOMODPROXY`) or checksum database (`GOSUMDB`).
**Recommendations**
Upgrade the base Go toolchain.
Users with a non-trusted `GOPROXY` can revalidate all dependencies of the current module by running "rm go.sum ; go mod tidy ; go mod verify".