pillarjs hbs up to 4.2.1 Async Helper cross site scripting

Summaryinfo

A vulnerability was found in pillarjs hbs up to 4.2.1 and classified as problematic. Affected by this issue is some unknown functionality of the component Async Helper. Such manipulation leads to cross site scripting. This vulnerability is referenced as CVE-2026-16231. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in pillarjs hbs up to 4.2.1. It has been rated as problematic. Affected by this issue is an unknown code of the component Async Helper. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. CVE summarizes:

hbs is an Express view engine that wraps Handlebars. Its registerAsyncHelper API bypasses Handlebars' automatic HTML escaping: an async helper returns an opaque placeholder during the first render pass, so the double-brace expression escapes only the placeholder, and after rendering hbs substitutes the placeholder with the raw callback return value without escaping it, across the cached, uncached, and layout render paths. An application that passes attacker-influenced data, for example user-supplied content from a database, into an async helper callback can therefore have arbitrary HTML and JavaScript injected into the server-rendered page, resulting in stored or reflected cross-site scripting. Versions 2.1.0 through 4.2.1 are affected, and the issue is fixed in 4.3.0, which HTML-escapes async helper output. Applications that intentionally emit raw HTML from an async helper can opt in explicitly with hbs.SafeString. Users should upgrade to 4.3.0.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-16231 since 07/18/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1059.007.

Upgrading to version 4.3.0 eliminates this vulnerability.

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Productinfo

Vendor

• pillarjs

Name

• hbs

Version

• 4.2.0
• 4.2.1

Website

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

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