{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Velocity.js is a JavaScript implementation of the Apache Velocity template engine. In 2.1.5 and earlier, a prototype pollution vulnerability was discovered in velocityjs. This issue occurs during the processing of #set directives in Velocity templates. If an application renders a template controlled by an attacker, it is possible to modify Object.prototype, potentially leading to Denial of Service (DoS) or Remote Code Execution (RCE) depending on the server environment."
    }
  ],
  "id": "CVE-2026-44966",
  "lastModified": "2026-05-26T22:16:43.293",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 8.3,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-05-26T22:16:43.293",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/shepherdwind/velocity.js/security/advisories/GHSA-j658-c2gf-x6pq"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-1321"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "velocityjs"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "2.1.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44966"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-09T00:40:16Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nA prototype pollution vulnerability was discovered in Velocity.js \u003c= 2.1.5. This issue occurs during the processing of #set directives in Velocity templates. If an application renders a template controlled by an attacker, it is possible to modify Object.prototype, potentially leading to Denial of Service (DoS) or Remote Code Execution (RCE) depending on the server environment.\n\n### Details\nThe root cause is located in the #set path assignment logic within the source code:\n- File: /src/compile/set.ts \n- Issue: The engine accepts arbitrary path keys and performs assignments using the logic `(baseRef as Record\u003cstring, unknown\u003e)[key] = val`.\n\n\nBecause there is no validation or filtering to block sensitive keys such as \\_\\_proto\\_\\_, constructor, or prototype, an attacker can traverse the prototype chain and pollute the global Object.prototype.\n\n### PoC\n```javascript\nconst {render} = require(\u0027velocityjs\u0027);\ndelete Object.prototype.polluted;\nconsole.log({}.polluted); // \"\"\nrender(\u0027#set($__proto__.polluted = \"hacked\")\u0027, {});\nconsole.log({}.polluted); // \"hacked\"\ndelete Object.prototype.polluted;\n```\n\n### Impact\n- Vulnerability Type: Prototype Pollution\n- Who is impacted: Any application that renders Velocity templates where the template content can be influenced or controlled by untrusted users.\n- Severity: High. Prototype pollution can often be used to bypass security controls, cause application crashes (DoS), or be chained with other vulnerabilities to achieve code execution.",
  "id": "GHSA-j658-c2gf-x6pq",
  "modified": "2026-05-09T00:40:16Z",
  "published": "2026-05-09T00:40:16Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/shepherdwind/velocity.js/security/advisories/GHSA-j658-c2gf-x6pq"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/shepherdwind/velocity.js"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Velocity.js has a Prototype Pollution vulnerability through #set path assignment"
}