TI-2026-26274 Aliases CVE-2026-33916 GHSA-2qvq-rjwj-gvw9

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

MEDIUM 55CWE-1321Published 2026-03-27 · Updated 2026-03-30

Key facts

Attack vector: Network
Privileges required: None
User interaction: Required
Attack complexity: High
Impact type: Cross-site scripting
Confidentiality · integrity · availability: Low · Low · None
Fix status: Partial Red Hat: 10 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-79.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.0028 20th percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Partial handlebars.js (handlebars-lang): 4.7.9handlebars (npm): 4.7.9Red Hat: 10 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
handlebars-lang	handlebars.js	4.0.0 to before 4.7.9	4.7.9	Patch available	CNA
—	handlebars (npm)	4.0.0 to before 4.7.9	4.7.9	Patch available	GHSA-2qvq-rjwj-gvw9

handlebars.js Vendorhandlebars-lang Affected 4.0.0 to before 4.7.9 Fixed in 4.7.9 Patch available CNA
handlebars (npm) Vendor— Affected 4.0.0 to before 4.7.9 Fixed in 4.7.9 Patch available GHSA-2qvq-rjwj-gvw9

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:handlebarsjs:handlebars::::::node.js::*	4.0.0 to before 4.7.9	Vulnerable	handlebars-lang

cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:* Versions 4.0.0 to before 4.7.9 Vulnerable ·handlebars-lang

Remediation

Fix · CNA handlebars.js (handlebars-lang) Fixed in 4.7.9
Fix · GHSA-2qvq-rjwj-gvw9 handlebars (npm) Fixed in 4.7.9 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Cryostat 4	Affected	No fix yet: Fix deferred
Logging Subsystem for Red Hat OpenShift	Affected	No fix yet: Fix deferred
Red Hat Data Grid 8	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 10	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 7	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 8	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 9	Affected	No fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)	Affected	No fix yet: Fix deferred
Red Hat OpenShift Dev Spaces	Affected	No fix yet: Fix deferred
Red Hat Process Automation 7	Affected	No fix yet: Fix deferred

Timeline

2026-10-02 Threatist record created from CVE-2026-33916
2026-10-03 Alias added: GHSA-2qvq-rjwj-gvw9

References

Exploit 1

https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2qvq-rjwj-gvw9

Patch 1

https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2

Advisory 3

Other 2

TI-2026-26288 Handlebars.js has JavaScript Injection via AST Type Confusion CVSS 3.1CRITICAL 9.8
TI-2026-26290 Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation CVSS 3.1HIGH 7.5
TI-2026-26292 Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options CVSS 3.1HIGH 8.3
TI-2026-26291 Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial CVSS 3.1HIGH 8.1
TI-2026-26289 Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block CVSS 3.1HIGH 8.1
TI-2021-06062 Remote code execution (RCE) in handlebars CVSS 3.1CRITICAL 9.8

See all 9 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences