GHSA-xm5m-wgh2-rrg3 — v2
MEDIUMGHSA-xm5m-wgh2-rrg3 is a medium-severity (CVSS 5.5) CWE-295 vulnerability in github.com/sigstore/timestamp-authority/v2. A fix is available for github.com/sigstore/timestamp-authority/v2 — see the affected versions and patch details below.
Sigstore Timestamp Authority has Improper Certificate Validation in verifier
Exploitation Status
No confirmed exploitation observed yet
- 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 GHSA-xm5m-wgh2-rrg3.
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.
How urgent is this, really
GHSA-xm5m-wgh2-rrg3 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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 | 2.0.6go get github.com/sigstore/timestamp-authority/v2@v2.0.6 |
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-xm5m-wgh2-rrg3 can be triaged on real exposure rather than presence alone.
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 Security finds GHSA-xm5m-wgh2-rrg3 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.