CVE-2026-33939

01/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.

02/Affected products

handlebarsjs: handlebars

03/References9

• github.com/handlebars-lang/handlebars.js/security/advisories/GH… ExploitVendor Advisory
• github.com/handlebars-lang/handlebars.js/security/advisories/GH… ExploitVendor Advisory
• github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26… Patch
• github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 Release Notes
• access.redhat.com/errata/RHSA-2026:10175
• access.redhat.com/errata/RHSA-2026:34342
• access.redhat.com/security/cve/CVE-2026-33939
• bugzilla.redhat.com/show_bug.cgi?id=2452508
• security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33939…