Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection

MITRE NVD CVE.ORG Print: PDF PDF

Summary

CVECVE-2026-33916
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-27 21:17:27 UTC
Updated2026-03-31 17:48:27 UTC
DescriptionHandlebars 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.

Risk And Classification

Primary CVSS: v3.1 4.7 MEDIUM from [email protected]

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

EPSS: 0.000390000 probability, percentile 0.116820000 (date 2026-04-01)

Problem Types: CWE-79 | CWE-1321 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | CWE-1321 CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary4.7MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
3.1[email protected]Secondary4.7MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
3.1CNADECLARED4.7MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS v3.1 Breakdown

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

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

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