CVE-2026-29063 Immutable.js: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in immutable
Prototype pollution in Immutable.js allows attackers to modify object prototypes, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-29063?
CVE-2026-29063 is a high-severity vulnerability in immutable-js, published on 6 Mar 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 versions 3.8.3, 4.3.7, and 5.1.5, Prototype Pollution is possible in immutable via the mergeDeep(), mergeDeepWith(), merge(), Map.toJS(), and Map.toObject() APIs. This issue has been patched in versions 3.8.3, 4.3.7, and 5.1.5.
Which versions are affected by CVE-2026-29063?
6 open source packages ship an affected version, including immutable. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
immutable npm | All versions | 3.8.3 |
immutable npm | All versions | 3.8.3 |
immutable npm | From 4.0.0-rc.1 | 4.3.8 |
immutable npm | From 4.0.0-rc.1 | 4.3.8 |
immutable npm | From 5.0.0 | 5.1.5 |
immutable npm | From 5.0.0 | 5.1.5 |
Products include Immutable-Js Immutable.
How do I fix CVE-2026-29063?
Upgrade immutable to a fixed version for your release line: 3.8.3, 4.3.8 or 5.1.5.
Is CVE-2026-29063 being exploited?
There is no known exploitation of CVE-2026-29063 in the wild and no public exploit code.
Other vulnerabilities in immutable-js
Sources
Also known as CLEANSTART-2026-YP71485, CLEANSTART-2026-ZU95238, CLSA-2026-1777509598, CLSA-2026-1782954035, CLSA-2026-1783040459, DEBIAN-CVE-2026-29063 and 10 more.