# CVE-2026-59879: Immutable.js denial of service via integer overflow in List component

Source: https://junglewise.ai/threats/cve-2026-59879-immutable-js-denial-of-service-via-integer-overflow-in-list  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-59879 · Severity: high · CVSS 7.5 · Published 2026-07-08

A vulnerability in the Immutable.js library, commonly used for managing data in web applications, can allow an attacker to crash a server or cause it to stop responding. By sending a specially crafted request containing a large index number, an attacker can trigger an infinite loop or memory exhaustion. This results in a denial-of-service (DoS) condition, potentially taking down websites or services that process untrusted user input using this library.

Technologies: [Immutable.js](https://junglewise.ai/threats/technologies/immutable-js), [immutable (npm)](https://junglewise.ai/threats/technologies/immutable). Vendors: [Immutable.js](https://junglewise.ai/threats/vendors/immutable-js), [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-59879 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59879 being exploited in the wild.

**How severe is CVE-2026-59879?** High severity, with a CVSS score of 7.5, published 8 July 2026.

**Which products and versions are affected?** Immutable.js < 4.3.9, >= 5.0.0-beta.1 < 5.1.8, < 4.3.9, >= 5.0.0-beta.1, < 5.1.8; immutable (npm) SEMVER:introduced=4.0.0-rc.1,fixed=4.3.9.

**Is there a fix for CVE-2026-59879?** Yes. immutable (npm): upgrade to 4.3.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-59879 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59879?** Check whether you run Immutable.js or immutable (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

- immutable (npm): upgrade to 4.3.9 or later

  ```sh
  npm install immutable@4.3.9
  ```


## Technical details

A vulnerability exists in Immutable.js 'List' operations (set, setSize, setIn, updateIn) due to the use of signed 32-bit bitwise arithmetic in the trie-based storage logic. When an index or size in the range [2^30, 2^31) is provided, the level-raising loop in 'setListBounds' encounters an integer overflow where the shift count (mod 32) causes the comparison to wrap, resulting in an infinite loop. On populated lists, this loop continuously allocates memory, leading to heap exhaustion and a process abort (SIGABRT/OOM-kill). The vulnerability can be triggered remotely if an application passes untrusted user input (like a numeric string from a URL or request body) directly into a List index or key-path. Patches are available in versions 4.3.9 and 5.1.8.

## Affected products

- Immutable.js immutable < 4.3.9, >= 5.0.0-beta.1, < 5.1.8

## Identifiers

- CVE-2026-59879
- GHSA-v56q-mh7h-f735

## Timeline

- 2026-06-25: disclosed
- 2026-07-08: advisory: NVD publication
- 2026-07-21: patched: GitHub Advisory updated with patch information

## References

- [https://api.github.com/users/mateuszismyname](https://api.github.com/users/mateuszismyname)
- [https://github.com/mateuszismyname](https://github.com/mateuszismyname)
- [https://api.github.com/users/mateuszismyname/gists%7B/gist_id%7D](https://api.github.com/users/mateuszismyname/gists%7B/gist_id%7D)
- [https://api.github.com/users/mateuszismyname/repos](https://api.github.com/users/mateuszismyname/repos)
- [https://avatars.githubusercontent.com/u/108668436?v=4](https://avatars.githubusercontent.com/u/108668436?v=4)
- [https://api.github.com/users/mateuszismyname/events%7B/privacy%7D](https://api.github.com/users/mateuszismyname/events%7B/privacy%7D)

## Related threats

- [Immutable.js denial of service via hash collision in Map and Set](https://junglewise.ai/threats/cve-2026-59880-immutable-js-denial-of-service-via-hash-collision-in-map-and-set)
- [Immutable.js Prototype Pollution in merge and Map APIs](https://junglewise.ai/threats/cve-2026-29063-immutable-js-prototype-pollution-in-merge-and-map-apis)