GHSA-xm5m-wgh2-rrg3
MEDIUMGHSA-xm5m-wgh2-rrg3 is a medium-severity (CVSS 5.5) CWE-295 vulnerability in github.com/sigstore/timestamp-authority/v2. O3 Security confirms whether GHSA-xm5m-wgh2-rrg3 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Sigstore Timestamp Authority has Improper Certificate Validation in verifier
Blast Radius
github.com/sigstore/timestamp-authority/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
Authorization bypass via certificate bag manipulation in sigstore/timestamp-authority verifier
An authorization bypass vulnerability exists in sigstore/timestamp-authority verifier (timestamp-authority/v2/pkg/verification): VerifyTimestampResponse function correctly verifies the certificate chain but when the TSA specific constraints are verified in VerifyLeafCert, the first non-CA certificate from the PKCS#7 certificate bag is used instead of the leaf certificate from the certificate chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key. The library validates the signature using the one certificate but performs authorization checks on the another, allowing an attacker to bypass some authorization controls.
This vulnerability does not apply to timestamp-authority service, only to users of timestamp-authority/v2/pkg/verification package.
This vulnerability does not apply to sigstore-go even though it is a user of timestamp-authority/v2/pkg/verification: Providing TSACertificate option to VerifyTimestampResponse fully mitigates the issue.
Patches
The issue will be fixed in timestamp-authority 2.0.6
Workarounds
Users of VerifyTimestampResponse can use the TSACertificate option to specify the exact certificate they expect to be used: this fully mitigates the issue.
References
This issue was found after reading CVE-2026-33753 / GHSA-3xxc-pwj6-jgrj (originally reported by @Jaynornj and @Pr00fOf3xpl0it)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/sigstore/timestamp-authority/v2 | all versions | 2.0.6 |
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/timestamp-authority/v2. 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/timestamp-authority/v2 to 2.0.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-xm5m-wgh2-rrg3 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-xm5m-wgh2-rrg3 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-xm5m-wgh2-rrg3. 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-xm5m-wgh2-rrg3 in your dependencies?
O3 detects GHSA-xm5m-wgh2-rrg3 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.