CVE-2026-31830: sigstore-ruby verifier returns success for DSSE bundles with mismatched in-toto subject digest
Summary
Sigstore::Verifier#verify does not propagate the VerificationFailure returned by verifyintoto when the artifact digest does not match the digest in the in-toto attestation subject. As a result, verification of DSSE bundles containing in-toto statements returns VerificationSuccess regardless of whether the artifact matches the attested subject.
Details
In lib/sigstore/verifier.rb, the verify method calls verifyintoto (line 176) without capturing or checking its return value:
verifyintoto(input, intoto)
When verifyintoto detects a digest mismatch, it returns a VerificationFailure object. Because the caller discards this return value, execution unconditionally falls through to return VerificationSuccess. This is the only verification sub-check in the method (out of 12) whose failure is not propagated.
The messagesignature code path is not affected.
Impact
An attacker who possesses a valid signed DSSE bundle containing an in-toto attestation for artifact A can present it as a valid attestation for a different artifact B. All other verification checks (DSSE envelope signature, certificate chain, Rekor inclusion, SCTs, policy) pass because they are independent of the artifact content. Only the in-toto subject digest check detects the mismatch, and its result is discarded.
This allows an attacker to bypass artifact-to-attestation binding for any consumer that relies on Sigstore::Verifier#verify to validate DSSE/in-toto bundles.
Workarounds
None. Consumers cannot work around this without patching the library.
Other sources
sigstore-ruby is a pure Ruby implementation of the sigstore verify command from the sigstore/cosign project. Prior to 0.2.3, Sigstore::Verifier#verify does not propagate the VerificationFailure returned by verifyintoto when the artifact digest does not match the digest in the in-toto attestation subject. As a result, verification of DSSE bundles containing in-toto statements returns VerificationSuccess regardless of whether the artifact matches the attested subject. This vulnerability is fixed in 0.2.3.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-31830?
CVE-2026-31830 is classified as a vulnerability that allows for verification failures in DSSE bundles due to mismatched subject digests.
How do I fix CVE-2026-31830?
To fix CVE-2026-31830, upgrade sigstore-ruby to version 0.2.3 or later to ensure proper verification of DSSE bundles.
What versions of sigstore-ruby are affected by CVE-2026-31830?
CVE-2026-31830 affects all versions of sigstore-ruby prior to 0.2.3.
What is the impact of CVE-2026-31830?
The impact of CVE-2026-31830 is that it allows incorrect verification results, potentially leading to unverified or malicious signatures being accepted.
Is CVE-2026-31830 a false positive issue?
No, CVE-2026-31830 is not a false positive; it represents a genuine risk of security verification failure.