CVE-2026-33939
Full vulnerability record from the local CVENow database.
Description
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.
Severity
HIGH
CVSS score
7.5
(v3.1)
Vulnerability status
Modified
Source identifier
Published
2026-03-27 22:16:20.857000
Last modified
2026-10-26 22:10:00.163000
View original CVE JSON
{
"id": "CVE-2026-33939",
"sourceIdentifier": "[email protected]",
"published": "2026-03-27T22:16:20.857",
"lastModified": "2026-10-26T22:10:00.163",
"vulnStatus": "Modified",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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."
},
{
"lang": "es",
"value": "Handlebars proporciona la potencia necesaria para permitir a los usuarios construir plantillas semánticas. En las versiones 4.0.0 a 4.7.8, cuando una plantilla de Handlebars contiene sintaxis de decorador que hace referencia a un decorador no registrado (por ejemplo, ’{{n}}’), la plantilla compilada llama a ’lookupProperty(decorators, ’n’)’, lo que devuelve ’undefined’. El tiempo de ejecución invoca inmediatamente el resultado como una función, causando un “TypeError” no manejado: ’... no es una función’ que bloquea el proceso de Node.js. Cualquier aplicación que compile plantillas proporcionadas por el usuario sin envolver la llamada en un “try/catch” es vulnerable a una denegación de servicio de una sola solicitud. La versión 4.7.9 corrige el problema. Algunas soluciones alternativas están disponibles. Envuelva la compilación y la renderización en “try/catch”. Valide la entrada de la plantilla antes de pasarla a “compile()”; rechace las plantillas que contengan sintaxis de decorador (’{{*...}}’) si los decoradores no se utilizan en su aplicación. Utilice el flujo de trabajo de precompilación; compile las plantillas en tiempo de compilación y sirva solo plantillas precompiladas; no llame a “compile()” en tiempo de solicitud."
}
],
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