# CVE-2026-4598: jsrsasign infinite loop in BigInteger.modInverse

Source: https://junglewise.ai/threats/cve-2026-4598-jsrsasign-infinite-loop-in-biginteger-modinverse  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-23. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-4598 · Severity: high · CVSS 7.5 · Published 2026-03-23

jsrsasign is a popular JavaScript library used for cryptography, including digital signatures and certificate processing. A flaw in how the library handles specific mathematical calculations allows an attacker to trigger an infinite loop, which permanently freezes the affected application. This results in a total denial of service, potentially crashing web servers or applications that rely on this library to process security tokens or encrypted data.

Technologies: [jsrsasign (npm)](https://junglewise.ai/threats/technologies/jsrsasign). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-4598 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-4598 being exploited in the wild.

**How severe is CVE-2026-4598?** High severity, with a CVSS score of 7.5, published 23 March 2026.

**Which products and versions are affected?** jsrsasign (npm) < 11.1.1, SEMVER:introduced=0,fixed=11.1.1.

**Is there a fix for CVE-2026-4598?** Yes. jsrsasign (npm): upgrade to 11.1.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-4598 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-4598?** Check whether you run jsrsasign (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- jsrsasign (npm): upgrade to 11.1.1 or later

  ```sh
  npm install jsrsasign@11.1.1
  ```


## Technical details

A vulnerability exists in the jsrsasign library (specifically within ext/jsbn2.js) due to an infinite loop in the BigInteger.modInverse implementation. The bnModInverse function fails to properly normalize negative inputs or handle zero as an input, causing the binary-GCD loop to never reach an exit condition. A remote, unauthenticated attacker can exploit this by providing crafted inputs to functions that utilize modular inversion, leading to 100% CPU utilization and a permanent hang of the JavaScript execution thread. The issue is fixed in version 11.1.1 by adding early return checks for zero and normalizing negative inputs using the mod(m) function.

## Affected products

- kjur jsrsasign < 11.1.1

## Identifiers

- CVE-2026-4598
- GHSA-8g7p-jf3g-gxcp

## Timeline

- 2026-02-20: patched: Fix merged into master branch via PR #648
- 2026-03-23: advisory: GitHub Advisory and NVD entry published

## References

- [https://github.com/kjur/jsrsasign/pull/648](https://github.com/kjur/jsrsasign/pull/648)
- [https://github.com/kjur/jsrsasign/commit/ca5b027240287a1e71fe63019fc4400332594323](https://github.com/kjur/jsrsasign/commit/ca5b027240287a1e71fe63019fc4400332594323)
- [https://gist.github.com/Kr0emer/a1bf5cd4547cc630d2dcc5e761de8264](https://gist.github.com/Kr0emer/a1bf5cd4547cc630d2dcc5e761de8264)
- [https://security.snyk.io/vuln/SNYK-JS-JSRSASIGN-15370938](https://security.snyk.io/vuln/SNYK-JS-JSRSASIGN-15370938)
- [https://access.redhat.com/errata/RHSA-2026:19375](https://access.redhat.com/errata/RHSA-2026:19375)

## Related threats

- [jsrsasign division by zero in RSA public key parsing](https://junglewise.ai/threats/cve-2026-4603-jsrsasign-division-by-zero-in-rsa-public-key-parsing)
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