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7.5
Sigstore Ruby Verifier Fails to Check Artifact Integrity
CVE-2026-31830
GHSA-mhg6-2q2v-9h2c
GHSA-mhg6-2q2v-9h2c
Summary
The Sigstore Ruby Verifier does not properly check the integrity of artifacts in DSSE bundles, allowing an attacker to present a valid signature for one artifact as if it were for a different artifact. This can lead to a security breach if your system relies on this verifier to validate the authenticity of artifacts. To mitigate this issue, update to a version of the Sigstore Ruby Verifier that includes the fix for this vulnerability.
What to do
- Update sigstore to version 0.2.3.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| – | sigstore | <= 0.2.3 | 0.2.3 |
Original title
sigstore-ruby verifier returns success for DSSE bundles with mismatched in-toto subject digest
Original description
### Summary
`Sigstore::Verifier#verify` does not propagate the `VerificationFailure` returned by `verify_in_toto` 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 `verify_in_toto` (line 176) without capturing or checking its return value:
`verify_in_toto(input, in_toto)`
When `verify_in_toto` 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 message_signature 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.
`Sigstore::Verifier#verify` does not propagate the `VerificationFailure` returned by `verify_in_toto` 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 `verify_in_toto` (line 176) without capturing or checking its return value:
`verify_in_toto(input, in_toto)`
When `verify_in_toto` 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 message_signature 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.
nvd CVSS3.1
7.5
Vulnerability type
CWE-252
Published: 11 Mar 2026 · Updated: 13 Mar 2026 · First seen: 10 Mar 2026