{"id":"CVE-2026-33939","aliases":["GHSA-9cx6-37pm-9jff"],"url":"https://o3.security/vulnerability/CVE-2026-33939","summary":"Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation","details":"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.","published":"2026-03-27T21:08:24.664Z","modified":"2026-09-06T03:30:45.682432326Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"handlebars","fixedVersion":"4.7.9"}],"fix":{"url":"https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2","label":"handlebars-lang/handlebars.js@68d8df5"},"references":[{"type":"WEB","url":"https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9"},{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33939.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:10175"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:34342"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-33939"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33939.json"},{"type":"ADVISORY","url":"https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-9cx6-37pm-9jff"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33939"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2452508"},{"type":"FIX","url":"https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-06T03:30:45.682432326Z"}}