GHSA-whqx-f9j3-ch6m
MEDIUMCosign verification accepts any valid Rekor entry under certain conditions
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/sigstore/cosign/v3🐹github.com/sigstore/cosign/v2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
A Cosign bundle can be crafted to successfully verify an artifact even if the embedded Rekor entry does not reference the artifact's digest, signature or public key. When verifying a Rekor entry, Cosign verifies the Rekor entry signature, and also compares the artifact's digest, the user's public key from either a Fulcio certificate or provided by the user, and the artifact signature to the Rekor entry contents. Without these comparisons, Cosign would accept any response from Rekor as valid. A malicious actor that has compromised a user's identity or signing key could construct a valid Cosign bundle by including any arbitrary Rekor entry, thus preventing the user from being able to audit the signing event.
This vulnerability only affects users that provide a trusted root via --trusted-root or when fetched automatically from a TUF repository, when no trusted key material is provided via SIGSTORE_REKOR_PUBLIC_KEY. When using the default flag values in Cosign v3 to sign and verify (--use-signing-config=true and --new-bundle-format=true for signing, --new-bundle-format=true for verification), users are unaffected. Cosign v2 users are affected using the default flag values.
This issue had previously been fixed in https://github.com/sigstore/cosign/security/advisories/GHSA-8gw7-4j42-w388 but recent refactoring caused a regression. We have added testing to prevent a future regression.
Steps to Reproduce
echo blob > /tmp/blob
cosign sign-blob -y --new-bundle-format=false --bundle /tmp/bundle.1 --use-signing-config=false /tmp/blob
cosign sign-blob -y --new-bundle-format=false --bundle /tmp/bundle.2 --use-signing-config=false /tmp/blob
jq ".rekorBundle |= $(jq .rekorBundle /tmp/bundle.2)" /tmp/bundle.1 > /tmp/bundle.3
cosign verify-blob --bundle /tmp/bundle.3 --certificate-identity-regexp='.*' --certificate-oidc-issuer-regexp='.*' /tmp/blob
Patches
Upgrade to Cosign v2.6.2 or Cosign v3.0.4. This does not affect Cosign v1.
Workarounds
You can provide trusted key material via a set of flags under certain conditions. The simplest fix is to upgrade to the latest Cosign v2 or v3 release.
Note that the example below works for cosign verify, cosign verify-blob, cosign verify-blob-attestation, and cosign verify-attestation`.
SIGSTORE_REKOR_PUBLIC_KEY=<path to Rekor pub key> cosign verify-blob --use-signing-config=false --new-bundle-format=false --bundle=<path to bundle> <artifact>
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/sigstore/cosign/v3 | all versions | 3.0.4 |
| 🐹Go | github.com/sigstore/cosign/v2 | all versions | 2.6.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sigstore/cosign/v3. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/sigstore/cosign/v3 to 3.0.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-whqx-f9j3-ch6m 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.
How O3 protects you
O3 pinpoints whether GHSA-whqx-f9j3-ch6m is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-whqx-f9j3-ch6m. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-whqx-f9j3-ch6m in your dependencies?
O3 detects GHSA-whqx-f9j3-ch6m across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.