Handlebars provides the power necessary to let users build semantic templates. From 3.0.0 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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
Present
Additional conditions required
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
High
Complete denial of service
CVSS Vector v4.0
Vulnerable Products
handlebars-lang:handlebars.js
References 4
https://github.com/handlebars-lang/handlebars.js/commit/ceec388abe1d1aac8f63698…
security-advisories@github.com
https://github.com/handlebars-lang/handlebars.js/pull/2185
security-advisories@github.com
https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.10
security-advisories@github.com
https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-…
security-advisories@github.com