pillarjs hbs up to 4.3.0 Async Helper toHTML denial of service

Summaryinfo

A vulnerability was found in pillarjs hbs up to 4.3.0 and classified as problematic. Affected by this issue is the function toHTML of the component Async Helper. Such manipulation leads to denial of service. This vulnerability is uniquely identified as CVE-2026-87123. The attack can be launched remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in pillarjs hbs up to 4.3.0. Affected by this issue is the function toHTML of the component Async Helper. The manipulation with an unknown input leads to a denial of service vulnerability. Using CWE to declare the problem leads to CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. Impacted is availability. CVE summarizes:

hbs is an Express view engine wrapper for Handlebars. Version 4.3.0 can crash the Node.js process during output escaping when an async helper, registered with registerAsyncHelper, resolves to an object whose toHTML property is truthy but not callable. Handlebars escapeExpression calls the toHTML method on any value that has a truthy toHTML, so such a value throws a TypeError, and because the async substitution runs on a later tick outside the render function's try/catch, the throw is an uncaught exception that terminates the process without sending a response. Only version 4.3.0 is affected, since the throwing escape was introduced by the fix for CVE-2026-16231 and earlier versions do not escape async helper values. It can be triggered remotely when an async helper resolves to an externally influenced object such as parsed JSON. The issue is fixed in hbs 4.3.1, and users should upgrade to hbs 4.3.1 or later.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-87123 since 09/08/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 4.3.1 eliminates this vulnerability.

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Productinfo

Vendor

• pillarjs

Name

• hbs

Version

• 4.0
• 4.1
• 4.2
• 4.3.0

Website

• Product: https://github.com/pillarjs/hbs/

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