Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection
CVE-2026-33916 is fixed in node-handlebars on 1 platform by DEBIAN-CVE-2026-33916 (version 3:4.7.9-1), released March 27, 2026. It is not reported as exploited. Patch Radar priority: Routine.
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| node-handlebars · Debian 14 | 3:4.7.9-1 | DEBIAN-CVE-2026-33916 | Mar 27, 2026 |
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