CVE-2026-33916 Details
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.
A vulnerability in Handlebars versions 4.0.0 through 4.7.8 allows for prototype pollution, which can lead to cross-site scripting (XSS) attacks. The issue arises in the Handlebars runtime, specifically within the `resolvePartial()` function. This function resolves partial names by directly accessing `options.partials` without any safeguards against prototype-chain traversal. If an attacker can inject a string value into `Object.prototype` that corresponds to a partial reference in a template, the injected string will be rendered as the partial body without HTML escaping. This vulnerability can be exploited to execute scripts in the context of the user.
Users can upgrade to Handlebars version 4.7.9 or later, where this vulnerability has been patched. Alternatively, the Handlebars runtime-only build can be used, which does not compile templates and reduces the attack surface.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Mar 30, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-1321 | Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') | [email protected] |
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| handlebarsjs handlebars | >= 4.0.0, < 4.7.9 |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Mar 31, 2026 | Initial Analysis | [email protected] |
| Mar 27, 2026 | New CVE Received | [email protected] |