CVE-2026-106445: CWE-184: Incomplete List of Disallowed Inputs in handlebars-lang handlebars.js
Description
CVE-2026-106445 is a critical vulnerability in handlebars.js versions 4.0.0 through 4.7.9. It involves an incomplete deny list of disallowed inputs in the lookupProperty function, allowing prototype access bypass. This flaw permits an attacker who can render a controlled template with allowProtoMethodsByDefault enabled to execute arbitrary JavaScript code with server privileges. The issue is fixed in version 4.7.10.
CVSS v4.0
Score 9.2critical
Affected software
handlebars-lang
handlebars.js
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Handlebars.js versions from 4.0.0 up to but not including 4.7.10 have a vulnerability where lookupProperty returns Function.prototype.constructor before applying the prototype-access deny list. Because 'constructor' is an own property of Function.prototype, an attacker controlling a template and with allowProtoMethodsByDefault enabled can traverse from an accessible function through its prototype chain to Function.prototype and then obtain the Function constructor. This allows execution of attacker-controlled JavaScript code with the server application's privileges. The vulnerability is addressed in version 4.7.10.
Potential Impact
Successful exploitation allows an attacker to execute arbitrary JavaScript code on the server with the application's privileges, potentially leading to full server compromise or unauthorized actions within the application context.
Mitigation Recommendations
Upgrade handlebars.js to version 4.7.10 or later, where this vulnerability is fixed. No other mitigation is indicated by the vendor advisory.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-10-06T16:49:40.590Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6ac550de2cdf04f656d8a128
Added to database: 10/06/2026, 19:49:50 UTC
Last enriched: 10/06/2026, 20:03:42 UTC
Last updated: 10/06/2026, 20:28:33 UTC
Views: 3
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