CVE-2026-4602 jsrsasign: Negative Exponent Handling Leads to Signature Verification Bypass

What is CVE-2026-4602?

CVE-2026-4602 is a high-severity vulnerability in jsrsasign, published on 23 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Versions of the package jsrsasign before 11.1.1 are vulnerable to Incorrect Conversion between Numeric Types due to handling negative exponents in ext/jsbn2.js. An attacker can force the computation of incorrect modular inverses and break signature verification by calling modPow with a negative exponent.

Weakness: CWE-681

Which versions are affected by CVE-2026-4602?

2 open source packages ship an affected version, including jsrsasign. It affects 1 product.

Products include Kjur Jsrsasign.

How do I fix CVE-2026-4602?

Upgrade jsrsasign to 11.1.1 or later.

Is CVE-2026-4602 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-4602 exists.

Other vulnerabilities in jsrsasign

• CVE-2020-14967 RSA PKCS#1 decryption vulnerability with prepending zeros in jsrsasign Critical 9.8
• CVE-2020-14968 RSA-PSS signature validation vulnerability by prepending zeros in jsrsasign Critical 9.8
• CVE-2026-4601 jsrsasign: Missing cryptographic validation during DSA signing enables private key extraction Critical 9.4
• CVE-2026-4599 jsrsasign: Incomplete Comparison Allows DSA Private Key Recovery via Biased Nonce Generation Critical 9.3
• CVE-2026-4600 jsrsasign: DSA signatures or X.509 certificates can be forged via DSA domain-parameter validation in KJUR.crypto.DSA.setPublic Critical 9.1

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-8qwj-4jxw-m8jw.