CVE-2026-4601 is a critical cryptographic vulnerability discovered in the jsrsasign JavaScript library, specifically affecting versions before 11.1.1. The issue lies in the DSA (Digital Signature Algorithm) signing implementation within the KJUR.crypto.DSA.signWithMessageHash function. During the signing process, the library fails to properly handle cases where the signature components r or s become zero. Normally, cryptographic signing algorithms retry signature generation if invalid values occur to ensure security. However, jsrsasign emits an invalid signature without retrying, which is a missing cryptographic step. This flaw allows an attacker to exploit the invalid signature mathematically to recover the private key (x) used in the DSA signing process. The recovery of the private key completely compromises the cryptographic security, enabling attackers to forge signatures or decrypt sensitive data. The vulnerability can be exploited remotely without authentication or user interaction, but requires high attack complexity due to the need to manipulate signature generation. The CVSS 4.0 base score is 9.4, reflecting the critical impact on confidentiality and integrity with no availability impact. Although no known exploits are currently reported in the wild, the severity and nature of the vulnerability make it a significant threat to any applications or systems relying on jsrsasign for DSA signatures. The recommended remediation is to upgrade to jsrsasign version 11.1.1 or later, where this issue has been fixed by adding the missing cryptographic step to retry signature generation when invalid values occur.

The impact of CVE-2026-4601 is severe for organizations worldwide that use jsrsasign for cryptographic operations involving DSA signatures. The vulnerability allows attackers to recover private keys, which can lead to complete compromise of digital signature authenticity and confidentiality. This undermines trust in signed data, enabling attackers to forge signatures, impersonate legitimate entities, and potentially decrypt sensitive communications or data protected by the compromised keys. Systems relying on jsrsasign for secure authentication, code signing, or secure communications are at risk of data breaches, fraud, and unauthorized access. The lack of requirement for authentication or user interaction increases the threat surface, allowing remote exploitation. Although the attack complexity is high, motivated adversaries with sufficient resources can exploit this flaw, especially in high-value targets. The vulnerability could affect software supply chains, web applications, and any cryptographic protocols using vulnerable versions of jsrsasign, leading to widespread security failures if not promptly addressed.

To mitigate CVE-2026-4601, organizations should immediately upgrade all instances of jsrsasign to version 11.1.1 or later, where the missing cryptographic step has been implemented to prevent invalid signature emission. Developers should audit their codebases and dependencies to identify any use of vulnerable jsrsasign versions, including transitive dependencies in web applications and backend services. Implement strict cryptographic validation and error handling to detect and reject invalid signatures early. Consider integrating cryptographic libraries with formal verification or stronger security guarantees for critical applications. Monitor cryptographic key usage for anomalies that might indicate exploitation attempts. Additionally, rotate any private keys potentially exposed due to this vulnerability and revoke associated certificates if applicable. Employ runtime application self-protection (RASP) or web application firewalls (WAF) to detect unusual signature-related activities. Finally, maintain an up-to-date inventory of cryptographic components and stay informed about security advisories for timely patching.