CVE-2026-53540 Python-Multipart: Negative Content-Length in parse_form buffers the entire body in memory

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.31, parseform did not validate the Content-Length header before using it to bound its chunked read of the request body. A negative Content-Length turned the bounded read into a read-until-EOF, so the entire body was loaded...