`gh attestation verify` returns incorrect exit code during verification if no attestations are present

Summary

A bug in GitHub's Artifact Attestation CLI tool, gh attestation verify, may return an incorrect zero exit status when no matching attestations are found for the specified --predicate-type <value> or the default https://slsa.dev/provenance/v1 if not specified. This issue only arises if an artifact has an attestation with a predicate type different from the one provided in the command. As a result, users relying solely on these exit codes may mistakenly believe the attestation has been verified, despite the absence of an attestation with the specified predicate type and the tool printing a verification failure.

Users are advised to update gh to version v2.67.0 as soon as possible.

Initial report: https://github.com/cli/cli/issues/10418 Fix: https://github.com/cli/cli/pull/10421

Details

The gh attestation verify command fetches, loads, and attempts to verify attestations associated with a given artifact for a specified predicate type. If an attestation is found, but the predicate type does not match the one specified in the gh attestation verify command, the verification fails, but the program exits early.

Due to a re-used uninitialized error variable, when no matching attestations are found, the relevant function returns nil instead of an error, causing the program to exit with a status code of 0, which incorrectly suggests successful verification.

PoC

Run gh attestation verify with local attestations using the --bundle flag and specify a predicate type with --predicate-type that you know will not match any of the attestations the command will attempt to verify. Confirm that the command exits with a zero status code.

Impact

Users who rely exclusively on the exit status code of gh attestation verify may incorrectly verify an attestation when the attestation's predicate type does not match the specified predicate type in the command.