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

> An attacker can break signature verification by forcing incorrect modular inverse computations via negative exponents in the jsrsasign library.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Mar 2026
- **Updated:** 10 Sep 2026
- **Also known as:** GHSA-8qwj-4jxw-m8jw

## 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 (Incorrect Conversion between Numeric Types)

## Which versions are affected by CVE-2026-4602?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `jsrsasign` | npm | All versions | 11.1.1 |
| `jsrsasign` | npm | All versions | 11.1.1 |

Products: 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](https://insights.sbomify.com/CVE-2020-14967/): RSA PKCS#1 decryption vulnerability with prepending zeros in jsrsasign (critical 9.8)
- [CVE-2020-14968](https://insights.sbomify.com/CVE-2020-14968/): RSA-PSS signature validation vulnerability by prepending zeros in jsrsasign (critical 9.8)
- [CVE-2026-4601](https://insights.sbomify.com/CVE-2026-4601/): jsrsasign: Missing cryptographic validation during DSA signing enables private key extraction (critical 9.4)
- [CVE-2026-4599](https://insights.sbomify.com/CVE-2026-4599/): jsrsasign: Incomplete Comparison Allows DSA Private Key Recovery via Biased Nonce Generation (critical 9.3)
- [CVE-2026-4600](https://insights.sbomify.com/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)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4602 and fix it if it is affected.

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

Affected packages and fixed versions:
- jsrsasign (npm): affected all versions; fixed in 11.1.1
- jsrsasign (npm): affected all versions; fixed in 11.1.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-4602/ (Markdown: https://insights.sbomify.com/CVE-2026-4602/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4602
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4602
- OSV: https://osv.dev/vulnerability/CVE-2026-4602

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4602/
Summaries are generated and may contain mistakes; the official description above is the record.