What’s Vulnerable › Vulnerabilities

CVE-2026-59880: Immutable.js: Hash-collision algorithmic complexity denial of service in Immutable.Map/Set

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-08 · updated 2026-07-10
• Weakness: CWE-407

Description

Immutable.js provides many Persistent Immutable data structures. Prior to 4.3.9 and 5.1.8, Immutable.Map and Immutable.Set keep keys that share the same 32-bit hash in a HashCollisionNode collision bucket that is scanned linearly, allowing an attacker who controls keys inserted into a Map, such as through Immutable.Map(obj), Immutable.fromJS(obj), state.merge(userObject), or mergeDeep, to craft many colliding keys and degrade insertion and lookup to consume disproportionate CPU. This issue is fixed in versions 4.3.9 and 5.1.8.

Affected products

• immutable-js: before 4.3.9; from 5.0.0 before 5.1.8 — fixed in 4.3.9, 5.1.8
• Npm Immutable: from 4.0.0-beta.1 before 4.3.9; from 5.0.0-beta.1 before 5.1.8; before 3.8.4 — fixed in 4.3.9, 5.1.8, 3.8.4

How to fix

Upgrade to a fixed version: immutable-js 4.3.9, 5.1.8; Npm Immutable 4.3.9, 5.1.8, 3.8.4. Check the vendor advisory for mitigations.

References

• https://github.com/immutable-js/immutable-js/commit/3dd7e5655012597a41873e328bf9142a8901527b
• https://github.com/immutable-js/immutable-js/commit/e51d49fc612ded5ec4dfb94ff294d22074269b0f
• https://github.com/immutable-js/immutable-js/releases/tag/v4.3.9
• https://github.com/immutable-js/immutable-js/releases/tag/v5.1.8
• https://github.com/immutable-js/immutable-js/security/advisories/GHSA-xvcm-6775-5m9r
• https://github.com/immutable-js/immutable-js/security/advisories/GHSA-xvcm-6775-5m9r

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