Affected: npm: form-data

## Summary

`form-data` builds `multipart/form-data` request bodies. Through v4.0.5, the `field` name passed to `FormData#append` and the `filename` option are concatenated directly into the `Content-Disposition` header with no escaping of CR (`\r`), LF (`\n`), or `"`. An application that uses **untrusted input as a field name or filename** therefore lets an attacker terminate the header line and either inject additional headers or smuggle whole additional multipart parts into the request the application forwards to a backend.

This is CWE-93 (CRLF injection). It is a divergence from how browsers and the WHATWG HTML spec serialize form-data (they escape these characters), so the fix is to match that behavior. Severity is **conditional**: it depends on the consuming application passing attacker-controlled data as a field name or filename. Applications that only use fixed/trusted field names are not affected.

## Details

In `lib/form_data.js`, `_multiPartHeader` builds the part header as:

```javascript 'Content-Disposition': ['form-data', 'name="' + field + '"'].concat(contentDisposition || []) ```

and `_getContentDisposition` builds `filename="' + filename + '"'`. Neither escapes control characters, so a `\r\n` in `field`/`filename` ends the header line. The same applies to `"`, which can break out of the quoted parameter.

### Proof of concept

```javascript const FormData = require('form-data'); const form = new FormData(); form.append('email"\r\nX-Injected: true\r\nfake…