Package Instance

BadHost: Missing Host header validation poisons request.url.path, bypassing path-based security checks
Starlette reconstructs the requested URL based on the HTTP Host request header and requested path, but does not perform any validation of the Host header value. This allows attackers to inject paths into the host part, prepending the actual path. However, routing in Starlette is based on the actual request path. This inconsistent interpretation of HTTP requests may lead to issues such as authentication bypass when the authentication depends on the reconstructed URL’s path.

Starlette vulnerable to O(n^2) DoS via Range header merging in ``starlette.responses.FileResponse``
An unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's `FileResponse` Range parsing/merging logic. This enables CPU exhaustion per request, causing denial‑of‑service for endpoints serving files (e.g., `StaticFiles` or any use of `FileResponse`).

Starlette Denial of service (DoS) via multipart/form-data
Starlette treats `multipart/form-data` parts without a `filename` as text form fields and buffers those in byte strings with no size limit. This allows an attacker to upload arbitrary large form fields and cause Starlette to both slow down significantly due to excessive memory allocations and copy operations, and also consume more and more memory until the server starts swapping and grinds to a halt, or the OS terminates the server process with an OOM error. Uploading multiple such requests in parallel may be enough to render a service practically unusable, even if reasonable request size limits are enforced by a reverse proxy in front of Starlette.

Starlette has possible denial-of-service vector when parsing large files in multipart forms
When parsing a multi-part form with large files (greater than the [default max spool size](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/formparsers.py#L126)) `starlette` will block the main thread to roll the file over to disk. This blocks the event thread which means we can't accept new connections.