Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation

{
  "id": "94666b9ee1e95c8da253cbfe4db2a50d0ad8b964bead96aea19aaa26a5a1278c",
  "url": "https://osv.dev/vulnerability/CVE-2026-33939",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation",
    "summary": "Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, when a Handlebars template contains decorator syntax referencing an unregistered decorator (e.g. `{{*n}}`), the compiled template calls `lookupProperty(decorators, \"n\")`, which returns `undefined`. The runtime then immediately invokes the result as a function, causing an unhandled `TypeError: ... is not a function` that crashes the Node.js process. Any application that compiles user-supplied templates without wrapping the call in a `try/catch` is vulnerable to a single-request Denial of Service. Version 4.7.9 fixes the issue. Some workarounds are available. Wrap compilation and rendering in `try/catch`. Validate template input before passing it to `compile()`; reject templates containing decorator syntax (`{{*...}}`) if decorators are not used in your application. Use the pre-compilation workflow; compile templates at build time and serve only pre-compiled templates; do not call `compile()` at request time.",
    "evidence": "osv:CVE-2026-33939",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-33939",
      "aliases": [
        "CVE-2026-33939",
        "GHSA-9cx6-37pm-9jff"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "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-2026-33939.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.360321154Z",
      "provider": "osv",
      "references": [
        "https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9",
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33939.json",
        "https://access.redhat.com/errata/RHSA-2026:10175",
        "https://access.redhat.com/errata/RHSA-2026:34342",
        "https://access.redhat.com/security/cve/CVE-2026-33939",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33939.json",
        "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-9cx6-37pm-9jff",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-33939",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2452508",
        "https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-754"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33939.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-33939",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 519745,
  "published_at": "2026-03-27T21:08:24.664+00:00"
}