CVE-2026-33916
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 3.1
- 4.7
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N - EPSS
- 0.3% chance of exploitation in the next 30 days; higher than 20% of CVEs (scores of 2026-10-26)
- CWEs
- CWE-79, CWE-1321
- Published
- Modified
- Record from
- the NVD, synced
Affected
- handlebarsjs:handlebars
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-2qvq-rjwj-gvw9 | npm | handlebars | >=4.0.0 <4.7.9 | 4.7.9 |