CVE-2026-33939

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.

Weakness classification

• security-advisories@github.com: CWE-754
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c: CWE-248

Primary references

• security-advisories@github.com — Patch
• security-advisories@github.com — Release Notes
• security-advisories@github.com — Exploit, Vendor Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
• 134c704f-9b21-4f2e-91b3-4a467353bcc0 — Exploit, Vendor Advisory
• 0b0ca135-0b70-47e7-9f44-1890c2a1c46c