Vulnerability · Published Mar 27, 2026 · Assigned by GitHub_M
CVE-2026-33993Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()
Medium 6.9
In plain English
A medium-severity prototype pollution in locutus from locutusjs. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 48% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. Prior to version 3.0.25, the `unserialize()` function in `locutus/php/var/unserialize` assigns deserialized keys to plain objects via bracket notation without filtering the `__proto__` key. When a PHP serialized payload contains `__proto__` as an array or object key, JavaScript's `__proto__` setter is invoked, replacing the deserialized object's prototype with attacker-controlled content. This enables property injection, for...in propagation of injected properties, and denial of service via built-in method override. This is distinct from the previously reported prototype pollution in `parse_str` (GHSA-f98m-q3hr-p5wq, GHSA-rxrv-835q-v5mh) — `unserialize` is a different function with no mitigation applied. Version 3.0.25 patches the issue.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | locutus | 3.0.25 | GHSA-4mph-v827-f877 |
Affected products (as reported)
Weakness: CWE-1321 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
References
- https://github.com/locutusjs/locutus/security/advisories/GHSA-4mph-v827-f877 x_refsource_CONFIRM
- https://github.com/locutusjs/locutus/pull/597 x_refsource_MISC
- https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4 x_refsource_MISC
- https://github.com/locutusjs/locutus/releases/tag/v3.0.25 x_refsource_MISC