Vulnerability Description
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 Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Handlebarsjs | Handlebars | >= 4.0.0, < 4.7.9 |
Related Weaknesses (CWE)
References
- https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084cPatch
- https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9Release Notes
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2qvq-rExploitVendor Advisory
FAQ
What is CVE-2026-33916?
CVE-2026-33916 is a vulnerability with a CVSS score of 4.7 (MEDIUM). 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...
How severe is CVE-2026-33916?
CVE-2026-33916 has been rated MEDIUM with a CVSS base score of 4.7/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-33916?
Check the references section above for vendor advisories and patch information. Affected products include: Handlebarsjs Handlebars.