CVE-2026-59879: 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, 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.

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.