Reported by GitHub_M · Published April 2, 2026
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit. For file parts, the uploaded body is written directly to a temporary file on disk rather than being constrained by the buffered in-memory upload limit. An unauthenticated attacker can therefore stream an arbitrarily large multipart file upload and consume unbounded disk space. This results in a denial of service condition for Rack applications that accept multipart form data. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
| Vendor | Product | Versions |
|---|---|---|
| rack | rack | < 2.2.23, >= 3.0.0.beta1, < 3.1.21, >= 3.2.0, < 3.2.6 |
| rack | rack | < 2.2.23, >= 3.0.0.beta1, < 3.1.21, >= 3.2.0, < 3.2.6 |