CVE-2026-33939: 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 de...

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.53%

40.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-754

Affected Software

Vendor	Product	Versions
Handlebarsjs	Handlebars	>= 4.0.0, < 4.7.9

References

https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2Patch
https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9Release Notes
https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-9cx6-37pm-9jffExploit, Vendor Advisory
https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-9cx6-37pm-9jffExploit, Vendor Advisory

Timeline

Published: Mar 27, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-33939?

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.

How severe is CVE-2026-33939?

CVE-2026-33939 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.53% probability of exploitation in the next 30 days.

How do I fix CVE-2026-33939?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.