CVE-2026-106445 · GHSA-p8wg-vrv2-v86f

Handlebars: JavaScript Injection via Own Property Check Bypass

Risk score: 77/100
CVSS: 9.2 v4.0
Exploit chance (30 days): 0.4%
Published: 6 Oct 2026

Open in the live forecast Today's forecast

What to know

What it is: 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 …
Affected: handlebars (npm) >= 3.0.0, <= 4.7.9
Fix: Upgrade handlebars to 4.7.10 or later.
Exploitation: Public proof of concept

Story map

Story map: the flaws, the fix, how it unfolded and what it connects to. Boxes link to the record or article.

At a glance

handlebars: Red, act today. Handlebars provides the power necessary to let users build semantic templates. From 4.0.0 until 4.7.10, Handlebars.compile() and Handlebars.precompile() accept pre-parsed AST objects while validating only selected PathExpression, NumberLiteral, and BooleanLiteral values. This issue bypasses the AST validation introduc…

The flaws

CVE-2026-106445: Handlebars: JavaScript Injection via Own Property Check Bypass (CVSS 9.2 · EPSS 0%)
CVE-2026-106446: Handlebars: JavaScript Injection via AST Type Confusion in compile (bypass of CVE-2026-33937) (CVSS 9.8 · EPSS 1%)
CVE-2026-106444: Handlebars: JavaScript Injection via Unsafe Inline Embedding of Precompiled Templates (CVSS 4.7 · EPSS 0%)

The fix

Upgrade handlebars: 4.7.10 or later on your release line

Who is exposed: handlebars (npm) >= 4.0.0, <= 4.7.9

Where it stands

Public proof of concept

Connects to

Same weakness: CWE-184 (CWE-184). 31 other warnings in 30 days

Why it is Amber

CVSS 9.2 critical
Public exploit or proof of concept referenced
Remotely exploitable without logging in
On your watchlist: npm

Affected packages

Package	Ecosystem	Vulnerable	Fixed in
handlebars	npm	>= 3.0.0, <= 4.7.9	4.7.10

References

Original description

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.

Last activity 6 Oct 2026. Patch Forecast updates every hour.