CVE-2026-31830 — sigstore
HIGHCVE-2026-31830 is a high-severity (CVSS 7.5) CWE-252 vulnerability in sigstore. A fix is available for sigstore — see the affected versions and patch details below.
sigstore-ruby verifier returns success for DSSE bundles with mismatched in-toto subject digest
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-31830.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
sigstoreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | sigstore | all versions | 0.2.3bundle update sigstore --conservative |
Affected Products
sigstoresigstoreDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for sigstore, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update sigstore to 0.2.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31830 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-31830 in your dependencies?
Find it across RubyGems, including transitive dependencies.