External risk intelligence

jsrsasign Invalid RSA Signatures Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2021-30246

This vulnerability exists in a Node.js software library (jsrsasign) used for cryptographic operations. Libraries are integrated into applications during development and are not public-facing network services themselves. The exposure depends entirely on how a developer implements the library within their specific application code.

Kjur Jsrsasign

10.1.13 and earlier

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability in the jsrsasign package for Node.js mistakenly validates certain invalid cryptographic signatures. While this flaw is critical, there is currently no known practical method to exploit it. The main concern is to determine if your organization uses this specific package and, if so, to confirm whether it has been integrated in a way that could potentially be affected.

Invalid signatures are accepted as valid.
Verify if this library is in use.
Confirm relevance and exposure.

Attack Path

How an attacker could exploit the issue

Attackers could reach this vulnerability by sending specially crafted data over a network to an application that uses the vulnerable jsrsasign package for cryptographic signature validation. If the application improperly handles these malformed signatures, it could mistakenly accept them as valid. This could potentially lead to unauthorized actions or data manipulation if the application relies on signature validity for access control or data integrity. The advisory notes that there is no known practical attack.

Requires network access to a vulnerable application.
Triggers when the application validates an invalid signature.
Risk of accepting forged signatures.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to have certain invalid RSA PKCS#1 v1.5 signatures mistakenly accepted as valid by applications using the affected library. This could potentially affect the integrity of cryptographic operations when signatures are relied upon for authentication or validation. However, the advisory notes that there is no known practical attack.

Cryptographic signature validation.
Invalid signatures could be accepted.
Integrity of validated data.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the jsrsasign package for Node.js impacts applications that use this library for RSA PKCS#1 v1.5 signature validation. Ownership typically lies with the application development or platform teams responsible for managing dependencies and their integration. The first practical step is to identify all applications utilizing this library, confirm their reachability and criticality, and then determine the accountable owner for remediation planning.

Application teams own the issue.
Verify affected application usage.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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Frequently asked questions

What is the jsrsasign package?

jsrsasign is a popular open-source JavaScript library designed for Node.js environments. Developers integrate it into their custom applications to perform complex cryptographic tasks, such as generating and verifying digital signatures or handling Public Key Infrastructure (PKI) data like certificates and RSA keys.

How does CVE-2021-30246 affect signature validation?

This vulnerability involves a weakness known as Improper Verification of Cryptographic Signature (CWE-347). Specifically, the library fails to correctly reject certain malformed RSA PKCS#1 v1.5 signatures. As a result, the code may incorrectly treat an invalid or forged signature as legitimate, which could compromise the trust placed in signed data.

Do I need a specific trigger to activate this flaw?

Yes. An attacker must send specially crafted data to an application that utilizes a vulnerable version of the library to perform signature checks. Importantly, the flaw is not triggered simply by the presence of the library; it only occurs if the application actively processes a malformed signature that bypasses the library's internal security checks.

Is my application at risk if it uses jsrsasign?

Halo Surface Signal indicates that because jsrsasign is a development library rather than a standalone network service, your specific exposure depends on how your developers have implemented it. An application is only potentially reachable if it exposes an interface that accepts and verifies external signatures over a network.

How should I respond to this vulnerability?

Start by identifying all applications within your environment that depend on jsrsasign versions 10.1.13 or earlier. Once identified, work with your development or platform teams to assess how these applications use the library for security decisions. Prioritize updates for systems that rely on these signatures to authorize access or maintain data integrity.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.