Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection

{
  "id": "395e3d49adf91cbaa6546972d94295c96bbf5bb53a5a931ddb9a1253235663d6",
  "url": "https://osv.dev/vulnerability/CVE-2026-33916",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection",
    "summary": "Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `resolvePartial()` in the Handlebars runtime resolves partial names via a plain property lookup on `options.partials` without guarding against prototype-chain traversal. When `Object.prototype` has been polluted with a string value whose key matches a partial reference in a template, the polluted string is used as the partial body and rendered without HTML escaping, resulting in reflected or stored XSS. Version 4.7.9 fixes the issue. Some workarounds are available. Apply `Object.freeze(Object.prototype)` early in application startup to prevent prototype pollution. Note: this may break other libraries, and/or use the Handlebars runtime-only build (`handlebars/runtime`), which does not compile templates and reduces the attack surface.",
    "evidence": "osv:CVE-2026-33916",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-33916",
      "aliases": [
        "CVE-2026-33916",
        "GHSA-2qvq-rjwj-gvw9"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/handlebars-lang/handlebars.js",
              "type": "GIT",
              "events": [
                {
                  "introduced": "bff5fab8f9d42e21950be00dcf1cedf4dc1a565b"
                },
                {
                  "fixed": "dce542c9a660048d31f0981ac8a45c08b919bddb"
                },
                {
                  "fixed": "68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:*",
                    "range": [
                      {
                        "introduced": "4.0.0"
                      },
                      {
                        "fixed": "4.7.9"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "dce542c9a660048d31f0981ac8a45c08b919bddb"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v4.7.9"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v4.7.8",
            "v4.7.7",
            "v4.7.6",
            "v4.7.5",
            "v4.7.4",
            "v4.7.3",
            "v4.7.2",
            "v4.7.1",
            "v4.7.0",
            "v4.6.0",
            "v4.5.3",
            "v4.5.2",
            "v4.5.1",
            "v4.5.0",
            "v4.4.3",
            "v4.4.2",
            "v4.4.1",
            "v4.2.1",
            "v4.3.4",
            "v4.4.0",
            "v4.3.3",
            "v4.3.2",
            "v4.3.1",
            "v4.3.0",
            "v4.2.0",
            "v4.1.2-0",
            "v4.1.2",
            "v4.1.1",
            "v4.0.12",
            "v4.0.11",
            "v4.0.10",
            "v4.0.9",
            "v4.0.8",
            "v4.0.7",
            "v4.0.6",
            "v4.0.5",
            "v4.0.4",
            "v4.0.3",
            "v4.0.2",
            "v4.0.1",
            "v4.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-33916.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.851454321Z",
      "provider": "osv",
      "references": [
        "https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33916.json",
        "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2qvq-rjwj-gvw9",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-33916",
        "https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1321",
          "CWE-79"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33916.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-33916",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 520202,
  "published_at": "2026-03-27T21:00:48.624+00:00"
}