# CVE-2026-4603: jsrsasign: Division by Zero Allows Invalid JWK Modulus to Cause Deterministic Zero Output in RSA Operations

> An attacker can cause denial of service and bypass security checks in jsrsasign by supplying a crafted JWK with a zero modulus.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Mar 2026
- **Updated:** 23 Mar 2026
- **Also known as:** GHSA-464q-cqxq-xhgr

## What is CVE-2026-4603?

CVE-2026-4603 is a medium-severity denial of service vulnerability in jsrsasign, published on 23 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Versions of the package jsrsasign before 11.1.1 are vulnerable to Division by zero due to the RSASetPublic/KEYUTIL parsing path in ext/rsa.js and the BigInteger.modPowInt reduction logic in ext/jsbn.js. An attacker can force RSA public-key operations (e.g., verify and encryption) to collapse to deterministic zero outputs and hide “invalid key” errors by supplying a JWK whose modulus decodes to zero.

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2026-4603?

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-2026-4603?

Upgrade jsrsasign to 11.1.1 or later.

## Is CVE-2026-4603 being exploited?

There is no known exploitation of CVE-2026-4603 in the wild and no public exploit code.

## 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-2026-4603 and fix it if it is affected.

What it is: CVE-2026-4603 is a medium-severity denial of service vulnerability in jsrsasign, published on 23 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-4603 in the wild and no public exploit code.

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-2026-4603/ (Markdown: https://insights.sbomify.com/CVE-2026-4603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4603
- OSV: https://osv.dev/vulnerability/CVE-2026-4603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4603/
Summaries are generated and may contain mistakes; the official description above is the record.