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CRITICAL severity

RSA signature validation vulnerability on maleable encoded message in jsrsasignGHSA-27fj-mc8w-j9wg

CRITICAL

GHSA-27fj-mc8w-j9wg is a critical-severity (CVSS 9.1) CWE-347 vulnerability in jsrsasign. A fix is available for jsrsasign — see the affected versions and patch details below.

Also known asCVE-2021-30246
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.0%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs60th percentile — riskier than 60% of all scored CVEsHighest risk
0.00%0.49%0.97%1.46%0.2%1.0%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-27fj-mc8w-j9wg by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.

jsrsasignnpm
1.2Mdownloads / week

Description

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

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmjsrsasignall versions10.2.0npm install jsrsasign@10.2.0

Affected Products

1 product · 1 configurations
Application
jsrsasignkjur
≤ 10.1.13
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jsrsasign, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. 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.

  3. 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

### 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
O3 Security · Impact-Aware SCA

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RSA signature validation vulnerability on maleable…