Skip to content
Heist/ feed
Back to feed
Medium

Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()

Type: advisorySources: OSV

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.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-33993
Confirmed fixed CVEs
Not specified
Updated in this feed
8 Nov 2026, 02:03 UTC · Revision 1

Source evidence

Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()

core-osv · Original source

Published 27 Mar 2026, 22:14 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.

osv:CVE-2026-33993
Complete source record
{
  "id": "d7690fc4aaa553f26e399d8a552f93ffd8305c02763273ec0654bd4d5cfc0f84",
  "url": "https://osv.dev/vulnerability/CVE-2026-33993",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()",
    "summary": "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.",
    "evidence": "osv:CVE-2026-33993",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-33993",
      "aliases": [
        "CVE-2026-33993",
        "GHSA-4mph-v827-f877"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/locutusjs/locutus",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "0d2402bdb92f9c59918114af9c8ba628f22e9152"
                },
                {
                  "fixed": "345a6211e1e6f939f96a7090bfeff642c9fcf9e4"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:locutus:locutus:*:*:*:*:*:node.js:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "3.0.25"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "345a6211e1e6f939f96a7090bfeff642c9fcf9e4"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "0d2402bdb92f9c59918114af9c8ba628f22e9152"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v3.0.25"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.0.24",
            "v3.0.23",
            "v3.0.22",
            "v3.0.21",
            "v3.0.20",
            "v3.0.19",
            "v3.0.18",
            "v3.0.17",
            "v3.0.16",
            "v3.0.15",
            "v3.0.14",
            "v3.0.13",
            "v3.0.12",
            "v3.0.11",
            "v3.0.10",
            "v3.0.9",
            "v3.0.8",
            "v3.0.7",
            "v3.0.6",
            "v3.0.5",
            "v3.0.4",
            "v3.0.3",
            "v3.0.2",
            "v3.0.1",
            "v3.0.0",
            "v2.0.39",
            "v2.0.38",
            "v2.0.37",
            "v2.0.36",
            "v2.0.35",
            "v2.0.34",
            "v2.0.33",
            "v2.0.32",
            "v2.0.30",
            "v2.0.29",
            "v2.0.28",
            "v2.0.27",
            "v2.0.26",
            "v2.0.25",
            "v2.0.24",
            "v2.0.23",
            "v2.0.22",
            "v2.0.21",
            "v2.0.20",
            "v2.0.19",
            "v2.0.17",
            "v2.0.16",
            "v2.0.15",
            "v2.0.14",
            "v2.0.13",
            "v2.0.12",
            "v2.0.11",
            "v2.0.10",
            "v2.0.9",
            "v2.0.8",
            "v2.0.7",
            "v2.0.6",
            "v2.0.5",
            "v2.0.4",
            "v2.0.3",
            "v2.0.2",
            "v2.0.1",
            "v2.0.0",
            "v1.3.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-33993.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:52.851394668Z",
      "provider": "osv",
      "references": [
        "https://github.com/locutusjs/locutus/releases/tag/v3.0.25",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33993.json",
        "https://github.com/locutusjs/locutus/security/advisories/GHSA-4mph-v827-f877",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-33993",
        "https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4",
        "https://github.com/locutusjs/locutus/pull/597"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1321"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33993.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-33993",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 521603,
  "published_at": "2026-03-27T22:14:03.495+00:00"
}