Handlebars.js has JavaScript Injection via AST Type Confusion

MITRE NVD CVE.ORG Print: PDF PDF

Summary

CVECVE-2026-33937
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-27 21:17:27 UTC
Updated2026-03-31 17:49:05 UTC
DescriptionHandlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `Handlebars.compile()` accepts a pre-parsed AST object in addition to a template string. The `value` field of a `NumberLiteral` AST node is emitted directly into the generated JavaScript without quoting or sanitization. An attacker who can supply a crafted AST to `compile()` can therefore inject and execute arbitrary JavaScript, leading to Remote Code Execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. Validate input type before calling `Handlebars.compile()`; ensure the argument is always a `string`, never a plain object or JSON-deserialized value. Use the Handlebars runtime-only build (`handlebars/runtime`) on the server if templates are pre-compiled at build time; `compile()` will be unavailable.

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.003240000 probability, percentile 0.553380000 (date 2026-04-01)

Problem Types: CWE-94 | CWE-843 | CWE-843 CWE-843: Access of Resource Using Incompatible Type ('Type Confusion') | CWE-94 CWE-94: Improper Control of Generation of Code ('Code Injection')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Handlebarsjs Handlebars All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Handlebars-lang Handlebars.js affected >= 4.0.0, < 4.7.9 Not specified

References

ReferenceSourceLinkTags
github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2w6w-6... [email protected] github.com Exploit, Vendor Advisory
github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 [email protected] github.com Release Notes
github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c... [email protected] github.com Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
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