CVE-2026-33993 Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()
Attackers can cause denial of service and property injection via prototype pollution in the unserialize function of the Locutus JavaScript library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33993?
CVE-2026-33993 is a medium-severity unsafe deserialization vulnerability in locutusjs locutus, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-1321
Which versions are affected by CVE-2026-33993?
2 open source packages ship an affected version, including locutus. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
locutus npm | All versions | 3.0.25 |
locutus npm | All versions | 3.0.25 |
Products include Locutus Locutus.
How do I fix CVE-2026-33993?
Upgrade locutus to 3.0.25 or later.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-33993 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33993 exists.
Other vulnerabilities in locutusjs locutus
- CVE-2026-32304 Locutus: RCE via unsanitized input in create_function()
- CVE-2020-7719 Prototype Pollution
- CVE-2026-25521 Locutus is vulnerable to Prototype Pollution
- CVE-2026-29091 Locutus: Remote Code Execution (RCE) in locutus call_user_func_array due to Code Injection
- CVE-2026-33994 Locutus Prototype Pollution due to incomplete fix for CVE-2026-25521
Sources
Also known as GHSA-4mph-v827-f877.