Axios is a promise based HTTP client for the browser and Node.js. From 1.0.0 to before 1.15.1, the FormDataPart constructor in lib/helpers/formDataToStream.js interpolates value.type directly into the Content-Type header of each multipart part without sanitizing CRLF (\r\n) sequences. An attacker who controls the .type property of a Blob/File-like object (e.g., via a user-uploaded file in a Node.js proxy service) can inject arbitrary MIME part headers into the multipart form-data body.

This bypasses Node.js v18+ built-in header protections because the injection targets the multipart body structure, not HTTP request headers. This vulnerability is fixed in 1.15.1.