GHSA-72gw-mp4g-v24j

### Impact

Multer is vulnerable to a Denial of Service (DoS) via deeply nested field names in multipart form data. The `append-field` dependency parses bracket notation in field names (e.g., `a[b][c]`) with no limit on nesting depth, allowing an attacker to force allocation of deeply nested object structures that consume CPU and memory. A single HTTP request with a crafted multipart body is sufficient to exploit this.

### Patches

Users should upgrade to `2.2.0` and configure `limits.fieldNestingDepth` to the minimum depth their application requires.

### Workarounds

Set `limits.fields` to a reasonable value to reduce the number of fields an attacker can send per request. This does not fully mitigate the issue but limits the impact.