GHSA-27fj-mc8w-j9wg
CRITICALGHSA-27fj-mc8w-j9wg is a critical-severity (CVSS 9.1) CWE-347 vulnerability in jsrsasign. O3 Security confirms whether GHSA-27fj-mc8w-j9wg is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
RSA signature validation vulnerability on maleable encoded message in jsrsasign
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
jsrsasignnpmDescription
Impact
Vulnerable jsrsasign will accept RSA signature with improper PKCS#1.5 padding.
Decoded RSA signature value consists following form:
01(ff...(8 or more ffs)...ff)00[ASN.1 OF DigestInfo]
Its byte length must be the same as RSA key length, however such checking was not sufficient.
To make crafted message for practical attack is very hard.
Patches
Users validating RSA signature should upgrade to 10.2.0 or later.
Workarounds
There is no workaround. Not to use RSA signature validation in jsrsasign.
ACKNOWLEDGEMENT
Thanks to Daniel Yahyazadeh @yahyazadeh for reporting and analyzing this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | jsrsasign | all versions | 10.2.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jsrsasign. 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 jsrsasign to 10.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-27fj-mc8w-j9wg 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-27fj-mc8w-j9wg 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-27fj-mc8w-j9wg. 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-27fj-mc8w-j9wg in your dependencies?
O3 detects GHSA-27fj-mc8w-j9wg across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.