CVE-2026-4598 Kjur CVE debrief

Who should care

Developers and administrators using the jsrsasign package, especially in Node.js environments, should be aware of this vulnerability. Given the high severity and potential for denial-of-service attacks, immediate attention is recommended for systems that have not been patched to version 11.1.1 or later.

Technical summary

The CVE-2026-4598 vulnerability is caused by a flaw in the bnModInverse function within the ext/jsbn2.js file of the jsrsasign package. This function is part of the BigInteger implementation and can enter an infinite loop when it receives zero or negative inputs. Specifically, calling modInverse(0, m) or modInverse(-1, m) can trigger this vulnerability, potentially allowing an attacker to cause a denial-of-service by hanging the process. The vulnerability affects all versions of jsrsasign before 11.1.1.

Defensive priority

High priority due to potential for denial-of-service attacks with CVSS score of 7.7

Recommended defensive actions

• Inventory affected systems using jsrsasign versions before 11.1.1
• Review official advisories for detailed mitigation strategies
• Apply the patch from version 11.1.1 or later
• Implement compensating controls to detect and prevent exploitation attempts
• Monitor systems for unusual activity indicative of potential exploitation

Evidence notes

The primary evidence for this vulnerability comes from the NVD and CVE records. The vulnerability affects jsrsasign versions before 11.1.1. The bnModInverse function's flaw allows for potential denial-of-service attacks. Defenders should verify the version of jsrsasign in use and ensure it is updated to 11.1.1 or later.

Official resources