Handlebars Improper Control of Generation of Code (Code Injection) Vulnerability - CVE-2026-33937

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8 Handlebars.compile() accepts a pre-parsed AST object in addition to a template string. The value field of a NumberLiteral AST node is emitted directly into the generated JavaScript without quoting or sanitization. An attacker who can supply a crafted AST to compile() can therefore inject and execute arbitrary JavaScript leading to Remote Code Execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. Validate input type before calling Handlebars.compile() ensure the argument is always a string never a plain object or JSON-deserialized value. Use the Handlebars runtime-only build (handlebars/runtime) on the server if templates are pre-compiled at build time compile() will be unavailable.