Bug 2452536 (CVE-2026-33993)

Summary: CVE-2026-33993 Locutus: Locutus: Prototype Pollution and Denial of Service vulnerability in unserialize() function
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: jcantril, rojacob
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Locutus, a library that integrates standard libraries from other programming languages into JavaScript. The `unserialize()` function, which converts serialized PHP data into JavaScript objects, fails to filter the `__proto__` key during deserialization. A remote attacker can exploit this by providing a specially crafted PHP serialized payload that includes `__proto__` as an array or object key. This vulnerability, known as prototype pollution, allows for property injection and can lead to a Denial of Service (DoS) by enabling attackers to override built-in JavaScript methods.
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Description OSIDB Bzimport 2026-03-27 23:02:28 UTC 
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.