CVE-2026-33916

CVE-2026-33916 · Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection

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, `resolvePartial()` in the Handlebars runtime resolves partial names via a plain property lookup on `options.partials` without guarding against prototype-chain traversal. When `Object.prototype` has been polluted with a string value whose key matches a partial reference in a template, the polluted string is used as the partial body and rendered without HTML escaping, resulting in reflected or stored XSS. Version 4.7.9 fixes the issue. Some workarounds are available. Apply `Object.freeze(Object.prototype)` early in application startup to prevent prototype pollution. Note: this may break other libraries, and/or use the Handlebars runtime-only build (`handlebars/runtime`), which does not compile templates and reduces the attack surface.

CVSS 4.7 · Medium · EPSS 0.3% · Fix available

Published

2026-03-27T21:00:48.624Z

Updated

2026-03-30T15:41:36.977Z

Stack: system · node

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