CVE-2026-31830 affects the sigstore-ruby library, a pure Ruby implementation of the sigstore verify command used for verifying software artifacts and their provenance via in-toto attestations. Prior to version 0.2.3, the method Sigstore::Verifier#verify does not correctly handle the return value from verify_in_toto when the artifact digest does not match the digest specified in the in-toto attestation subject. Specifically, the VerificationFailure returned by verify_in_toto is ignored, causing the verification process to incorrectly return VerificationSuccess. This means that DSSE (Dead Simple Signing Envelope) bundles containing in-toto statements can be accepted as valid even if the artifact has been tampered with or replaced, effectively bypassing the integrity check. The root cause is an unchecked return value vulnerability (CWE-252), where the failure condition is not propagated or handled properly. The vulnerability is remotely exploitable without any privileges or user interaction, making it a significant risk for supply chain security. The flaw was publicly disclosed on March 10, 2026, with a CVSS v3.1 score of 7.5 (high severity), reflecting its impact on integrity and ease of exploitation. The issue was fixed in sigstore-ruby version 0.2.3 by ensuring that verification failures are properly propagated and cause verification to fail as expected.

The primary impact of this vulnerability is the potential acceptance of malicious or altered software artifacts as legitimate and verified, which undermines the trust model of software supply chains relying on sigstore-ruby for artifact verification. Organizations using vulnerable versions may unknowingly deploy compromised software, leading to integrity breaches that can facilitate further attacks such as code injection, backdoors, or unauthorized access. Since sigstore is increasingly adopted for securing software provenance and supply chains, this vulnerability poses a significant risk to software developers, CI/CD pipelines, and downstream consumers globally. The lack of authentication or user interaction required to exploit the vulnerability increases the attack surface. While no known exploits are currently reported in the wild, the high severity and straightforward exploitation mean attackers could develop exploits rapidly. This could lead to widespread supply chain compromises, especially in environments that rely heavily on Ruby-based tooling or integrate sigstore-ruby for verification.

To mitigate this vulnerability, organizations should immediately upgrade sigstore-ruby to version 0.2.3 or later, where the issue is fixed. Additionally, users should audit their verification workflows to ensure that verification failures are properly checked and handled, preventing silent acceptance of invalid artifacts. Implementing additional integrity checks or secondary verification mechanisms can provide defense in depth. Monitoring software supply chain logs for anomalies or unexpected verification successes can help detect exploitation attempts. Organizations should also review their dependency management and CI/CD pipelines to confirm no vulnerable versions are in use. Finally, educating developers and security teams about the importance of handling return values and verification results correctly can prevent similar issues in custom tooling.