Vulnerability · Published Mar 27, 2026 · Assigned by GitHub_M
CVE-2026-33916Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection
Medium 4.7
In plain English
A medium-severity cross-site scripting in handlebars.js from handlebars-lang. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | node-handlebars | no fix listed | DEBIAN-CVE-2026-33916 |
| Debian:13 | node-handlebars | no fix listed | DEBIAN-CVE-2026-33916 |
| Debian:14 | node-handlebars | 3:4.7.9-1 | DEBIAN-CVE-2026-33916 |
| Ubuntu:22.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33916 |
| Ubuntu:24.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33916 |
| Ubuntu:25.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-33916 |
| Ubuntu:26.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33916 |
| Ubuntu:26.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-33916 |
| npm | handlebars | 4.7.9 | GHSA-2qvq-rjwj-gvw9 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| handlebars-lang | handlebars.js | >= 4.0.0, < 4.7.9 |
Weakness: CWE-79, CWE-1321 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
References
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2qvq-rjwj-gvw9 x_refsource_CONFIRM
- https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2 x_refsource_MISC
- https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 x_refsource_MISC