CVE-2026-33940

Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial

Published Mar 27, 2026 CVSS 3.1 · 8.1 High EPSS < 1% KEV · Not listed
Description
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, a crafted object placed in the template context can bypass all conditional guards in `resolvePartial()` and cause `invokePartial()` to return `undefined`. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to `env.compile()`. Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). Without `compile()`, the fallback compilation path in `invokePartial` is unreachable. Second, sanitize context data before rendering: Ensure no value in the context is a non-primitive object that could be passed to a dynamic partial. Third, avoid dynamic partial lookups (`{{> (lookup ...)}}`) when context data is user-controlled.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-xhpv-hc6g-r9c6 Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial
History
Type Values Removed Values Added
CPEs cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:*
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Handlebarsjs
Handlebarsjs handlebars
Vendors & Products Handlebarsjs
Handlebarsjs handlebars
Type Values Removed Values Added
Description Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, a crafted object placed in the template context can bypass all conditional guards in `resolvePartial()` and cause `invokePartial()` to return `undefined`. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to `env.compile()`. Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). Without `compile()`, the fallback compilation path in `invokePartial` is unreachable. Second, sanitize context data before rendering: Ensure no value in the context is a non-primitive object that could be passed to a dynamic partial. Third, avoid dynamic partial lookups (`{{> (lookup ...)}}`) when context data is user-controlled.
Title Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial
Weaknesses CWE-843
CWE-94
References
Metrics cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 4, 2026, 12:04 PM
Reserved
Mar 24, 2026, 7:50 PM
Status
Modified
Published
Mar 27, 2026, 10:16 PM
Modified
Oct 26, 2026, 10:10 PM
Severity
Important
Public date
Mar 27, 2026, 9:11 PM