CVE-2026-115927: Tornado: Event loop blocking and excess memory use from chunked bodies with many small chunks

When Tornado reads an HTTP/1.1 body that uses chunked transfer encoding, it processes all chunks that have already arrived without yielding to the event loop. A client can send a body made of millions of 1-byte chunks, which blocks the event loop (and therefore every other connection served by that process) for the entire time it takes to parse the body. A body near the default max_body_size of 100 MB can block the process for close to a minute, and the attacker can repeat or parallelize these requests.

Bodies made of tiny chunks also consumed far more memory than their size: a handler that does not use @stream_request_body stored each chunk as a separate object, using roughly 20 times as much memory as the bytes received.