CVE-2026-59880 Immutable.js: Hash-collision algorithmic complexity denial of service in Immutable.Map/Set
Attackers can cause CPU exhaustion in Immutable.js applications by inserting keys with colliding hashes into Maps or Sets.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59880?
CVE-2026-59880 is a high-severity denial of service vulnerability in immutable-js, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-407
Which versions are affected by CVE-2026-59880?
6 open source packages ship an affected version, including immutable. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
immutable npm | All versions | 3.8.4 |
immutable npm | All versions | 3.8.4 |
immutable npm | From 4.0.0-beta.1 | 4.3.9 |
immutable npm | From 4.0.0-beta.1 | 4.3.9 |
immutable npm | From 5.0.0-beta.1 | 5.1.8 |
immutable npm | From 5.0.0-beta.1 | 5.1.8 |
Products include Immutable-Js Immutable.
How do I fix CVE-2026-59880?
Upgrade immutable to a fixed version for your release line: 3.8.4, 4.3.9 or 5.1.8.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-59880 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59880 exists.
Other vulnerabilities in immutable-js
Sources
Also known as CLEANSTART-2026-BI32681, CLEANSTART-2026-VB50849, CLSA-2026-1784769617, CLSA-2026-1784856200, CLSA-2026-1784856463, CLSA-2026-1784943220 and 14 more.