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high7.5

CVE-2026-33939

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

Impact

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.

Affected packages

EcosystemPackageAffectedFixed in
npmhandlebars>= 4.0.0, <= 4.7.84.7.9

Affected products

VendorProductAffected versions
HandlebarsjsHandlebars
from 4.0.0 before 4.7.9

Weakness classification

CWE-754CWE-248

References