AIKIDO-2026-970464

TL;DR

Handlebars.compile() and Handlebars.precompile() accept a pre-parsed AST, and the validator only checks values on PathExpression, NumberLiteral, and BooleanLiteral nodes. Values such as Program.blockParams.length, the depth on a non-PathExpression param, or a non-string StringLiteral.value/PathExpression.original are written into the generated JavaScript unchecked. An untrusted AST, such as a parsed JSON request body, can insert arbitrary JavaScript into the generated output so it runs on the server with compile() or wherever the precompiled output later loads. The fix validates these values directly at each compiler write site and restricts node type dispatch to known node types.