Handlebars: JavaScript Injection via Own Property Check Bypass

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-106445
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-06 20:17:26 UTC
Updated2026-10-06 20:17:26 UTC
DescriptionHandlebars provides the power necessary to let users build semantic templates. From 4.0.0 until 4.7.10, Handlebars lookupProperty returns Function.prototype.constructor before applying the prototype-access deny list because constructor is an own property of Function.prototype. When an attacker can render a controlled template with allowProtoMethodsByDefault enabled and an accessible function in the template context, the template can traverse from that function through its prototype to Function.prototype and then obtain the Function constructor through the own-property bypass. This permits attacker-controlled JavaScript to execute with the server application's privileges. This issue is fixed in version 4.7.10.

Risk And Classification

Primary CVSS: v4.0 9.2 CRITICAL from [email protected]

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-184 | CWE-1289 | CWE-184 CWE-184: Incomplete List of Disallowed Inputs | CWE-1289 CWE-1289: Improper Validation of Unsafe Equivalence in Input

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary9.2CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED9.2CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
High
Integrity
High
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Handlebars-lang Handlebars.js affected >= 4.0.0, < 4.7.10 Not specified

References

ReferenceSourceLinkTags
github.com/handlebars-lang/handlebars.js/commit/ceec388abe1d1aac8f636986... [email protected] github.com
github.com/handlebars-lang/handlebars.js/pull/2185 [email protected] github.com
github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-v... [email protected] github.com
github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.10 [email protected] github.com
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