CVE-2026-59880: Immutable-Js Immutable

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

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 Immutable: before 4.3.9 (fixed in 4.3.9); from 5.0.0, before 5.1.8 (fixed in 5.1.8)

Published 2026-07-08. Last modified 2026-07-10.