Handlebars up to 4.7.8 Template Call compile unusual condition

Summaryinfo

A vulnerability identified as problematic has been detected in Handlebars up to 4.7.8. The affected element is the function compile of the component Template Call Handler. The manipulation leads to unusual condition. This vulnerability is documented as CVE-2026-33939. The attack can be initiated remotely. There is not any exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Handlebars up to 4.7.8. It has been rated as problematic. This issue affects the function compile of the component Template Call Handler. The manipulation with an unknown input leads to a unusual condition vulnerability. Using CWE to declare the problem leads to CWE-754. The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product. Impacted is availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-33939 since 03/24/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 304155 (Linux Distros Unpatched Vulnerability : CVE-2026-33939), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 4.7.9 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (304155). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• Handlebars

Version

• 4.7.0
• 4.7.1
• 4.7.2
• 4.7.3
• 4.7.4
• 4.7.5
• 4.7.6
• 4.7.7
• 4.7.8

License

• open-source

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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