aiohttp: CRLF injection in multipart headers

Summary

Attacker-controlled input included into multipart/payload headers can be used to modify a request to inject additional headers or similar.

Impact

In the unlikely situation that an application is passing user-controlled strings into MultipartWriter.append(headers=...) or Payload.headers, then an attacker may be able to modify the request to inject headers or change the contents of the request.

Workaround

Sanitise such user input.

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Patch: https://github.com/aio-libs/aiohttp/commit/bf88077ebb14f4c29924b8e8904cba20c55c28b8