CVE-2026-33940

CVE-2026-33940 · Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial

This page contains facts from public vulnerability sources. Check the original advisory before updating.

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, a crafted object placed in the template context can bypass all conditional guards in `resolvePartial()` and cause `invokePartial()` to return `undefined`. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to `env.compile()`. Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). Without `compile()`, the fallback compilation path in `invokePartial` is unreachable. Second, sanitize context data before rendering: Ensure no value in the context is a non-primitive object that could be passed to a dynamic partial. Third, avoid dynamic partial lookups (`{{> (lookup ...)}}`) when context data is user-controlled.

CVSS 8.1 · High · EPSS 0.7% · Fix available

Published

2026-03-27T21:11:10.719Z

Updated

2026-09-04T12:04:53.335Z

Stack: system · node

Check your server →