CVE-2026-33940

A flaw was found in Handlebars.js. A remote attacker can exploit this vulnerability by providing a specially crafted object within the template context. This crafted object, when processed by a dynamic partial lookup, can bypass security checks and be interpreted as malicious code. This allows the attacker to execute arbitrary commands on the server where Handlebars.js is running.

This is an Important arbitrary code execution vulnerability in Handlebars.js. The flaw can be exploited when an application uses Handlebars.js with dynamic partial lookups and processes user-controlled data within the template context. Red Hat products bundling Handlebars.js are affected if they meet these specific conditions for exploitation.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, use the runtime-only build of Handlebars.js, which prevents the fallback compilation path from being reached. Alternatively, sanitize all context data before rendering to ensure no non-primitive objects are passed to dynamic partials. Avoid dynamic partial lookups ({{> (lookup ...)}}) when context data is user-controlled. Implementing these mitigations may require application-level changes.