jsrsasign DSA Nonce Bias Vulnerability (CVE-2026-4599)

hello@craftedsignal.io — Thu, 18 Jan 2024 12:00:00 +0000

The jsrsasign library, a popular JavaScript cryptography toolkit, contains a critical vulnerability (CVE-2026-4599) in versions 7.0.0 up to, but not including, 11.1.1. This flaw resides in the getRandomBigIntegerZeroToMax and getRandomBigIntegerMinToMax functions within src/crypto-1.1.js. The vulnerability stems from incomplete comparison checks that accept out-of-range candidates when generating DSA nonces. This introduces a bias in the nonce generation process, which an attacker could exploit to potentially recover the private key associated with the DSA signatures. This is a high-severity issue because successful exploitation allows for complete compromise of the cryptographic keys.

Attack Chain

An attacker identifies a target application utilizing a vulnerable version (7.0.0 to 11.1.0) of the jsrsasign library for DSA signature generation.
The application calls the vulnerable getRandomBigIntegerZeroToMax or getRandomBigIntegerMinToMax function within src/crypto-1.1.js to generate a random nonce (k) for DSA signature creation.
Due to the incomplete comparison checks, the function generates a biased set of nonces, meaning some nonces are statistically more likely to be generated than others.
The attacker collects a significant number of DSA signatures generated by the vulnerable application.
The attacker analyzes the collected signatures, leveraging statistical analysis techniques to identify the bias in the generated nonces (k).
Using the identified nonce bias, the attacker applies mathematical algorithms (e.g., lattice-based techniques or Hidden Number Problem solvers) to recover the private key.
The attacker successfully reconstructs the private key used for signing.
The attacker can now forge signatures, impersonate the legitimate entity, and potentially gain unauthorized access or perform malicious actions.

Impact

Successful exploitation of CVE-2026-4599 allows an attacker to recover the private key used in DSA signature generation by applications using vulnerable versions of jsrsasign. This allows the attacker to forge signatures, potentially leading to unauthorized access, data breaches, and complete compromise of systems relying on the affected keys. The vulnerability has a CVSS v3.1 base score of 9.1, indicating critical severity. While the number of victims is unknown, any application relying on jsrsasign for DSA signatures is potentially vulnerable.

Recommendation

Upgrade the jsrsasign library to version 11.1.1 or later to patch CVE-2026-4599.
Implement the Sigma rule "Detect jsrsasign Vulnerable Version Usage" to identify systems using vulnerable versions of the library.
Monitor web server logs for requests containing potentially malicious DSA signature generation attempts, focusing on applications known to use jsrsasign.

jsrsasign DSA Signature Forgery Vulnerability (CVE-2026-4600)

hello@craftedsignal.io — Tue, 02 Jan 2024 10:00:00 +0000

A critical vulnerability, CVE-2026-4600, affects jsrsasign versions before 11.1.1. This flaw stems from insufficient validation of DSA domain parameters within the KJUR.crypto.DSA.setPublic function and related DSA/X509 verification processes in src/dsa-2.0.js. The vulnerability allows an attacker to forge DSA signatures or X.509 certificates. By supplying malicious domain parameters (e.g., g=1, y=1, fixed r=1), an attacker can manipulate the verification equation to evaluate as true, irrespective of the actual hash value. This can lead to successful verification of a forged signature by X509.verifySignature(). This poses a significant risk, as it can be exploited to bypass authentication mechanisms or install malicious software that appears to be legitimately signed.

Attack Chain

An attacker crafts a malicious DSA key pair, manipulating the domain parameters g, y, and r to specific values (e.g., g=1, y=1, r=1).
The attacker uses this maliciously crafted key to forge a DSA signature for arbitrary data.
The forged signature, along with the manipulated DSA public key, is presented to an application using a vulnerable version of jsrsasign.
The application calls KJUR.crypto.DSA.setPublic with the attacker-controlled public key, which contains the malicious domain parameters.
The application attempts to verify the forged signature using X509.verifySignature().
Due to the improper validation of DSA domain parameters, the verification equation evaluates to true regardless of the hash of the signed data.
The application incorrectly accepts the forged signature as valid.
The attacker gains unauthorized access to resources or executes arbitrary code, relying on the successful verification of the forged signature.

Impact

Successful exploitation of CVE-2026-4600 can have severe consequences. An attacker can forge digital signatures, potentially allowing them to bypass security controls, impersonate legitimate entities, or distribute malicious software that appears to be trusted. This can lead to widespread compromise, data breaches, and significant reputational damage. The vulnerability impacts any application using the vulnerable jsrsasign library for DSA signature verification, particularly those relying on X.509 certificates for authentication and authorization.

Recommendation

Upgrade the jsrsasign package to version 11.1.1 or later to remediate CVE-2026-4600.
Deploy the Sigma rule "Detect DSA Public Key with Suspicious Parameters" to identify attempts to use DSA public keys with g=1 and y=1 in your environment.
Monitor web server logs (category: webserver, product: linux) for suspicious requests involving DSA signature verification, particularly those using parameters like g=1, y=1, and r=1.

Jsrsasign - CraftedSignal Threat Feed

jsrsasign DSA Nonce Bias Vulnerability (CVE-2026-4599)

Attack Chain

Impact

Recommendation

jsrsasign DSA Signature Forgery Vulnerability (CVE-2026-4600)

Attack Chain

Impact

Recommendation