CVE-2026-33937

The handlebars package before 4.0.0 for Node.js allows remote attackers to conduct cross-site scripting (XSS) attacks by leveraging a template with an attribute that is not quoted.

Handlebars from 4.0.0 to 4.7.10 accepts pre-parsed AST objects in compile() and precompile() while validating only selected values. An attacker who can supply an object instead of a template string can place JavaScript expressions in unchecked values, leading to code execution on the server. Applications that pass only template strings are not affected. Fixed in 4.7.10.

Handlebars versions from 3.0.0 to 4.7.10 are vulnerable because lookupProperty returns Function.prototype.constructor before applying the prototype-access deny list. An attacker who can render a controlled template with allowProtoMethodsByDefault enabled can access the Function constructor via a bypass, allowing attacker-controlled JavaScript to execute with the server application's privileges.

The package handlebars before 4.7.7 is vulnerable to Prototype Pollution when selecting certain compiling options to compile templates coming from an untrusted source.

The package handlebars before 4.7.7 are vulnerable to Remote Code Execution (RCE) when selecting certain compiling options to compile templates coming from an untrusted source.

Versions of handlebars prior to 4.3.0 are vulnerable to Prototype Pollution leading to Remote Code Execution. Templates may alter an Object's __proto__ and __defineGetter__ properties, which may allow an attacker to execute arbitrary code through crafted payloads.

In Handlebars from 4.0.0 until 4.7.10, Handlebars.precompile() uses quotedString() to emit static template text into generated JavaScript without escaping sequences that terminate an enclosing HTML script element. When an application precompiles attacker-controlled template text and embeds the generated source in an inline script element, a closing script delimiter can end the element and cause following markup to be parsed and executed.

A vulnerability in the Handlebars CLI precompiler (versions 4.0.0 through 4.7.8) allows arbitrary JavaScript injection via unsanitized template filenames and CLI arguments. An attacker can execute arbitrary code in Node.js or browser environments when the generated bundle is loaded.

A vulnerability in Handlebars versions 4.0.0 through 4.7.8 allows an attacker to achieve remote code execution on the server by injecting a crafted object into the template context. The object bypasses security checks in `resolvePartial()` and causes `env.compile()` to compile malicious JavaScript. The issue is fixed in version 4.7.9.

A vulnerability in Handlebars versions 4.0.0 through 4.7.8 causes a Node.js process crash when processing a template with an unregistered decorator. A TypeError occurs when the runtime attempts to invoke an undefined value as a function.