python-multipart has a Denial of service (DoS) via deformation `multipart/form-data` boundary

Vulnerability Description

python-multipart is a streaming multipart parser for Python. When parsing form data, python-multipart skips line breaks (CR \r or LF \n) in front of the first boundary and any tailing bytes after the last boundary. This happens one byte at a time and emits a log event each time, which may cause excessive logging for certain inputs. An attacker could abuse this by sending a malicious request with lots of data before the first or after the last boundary, causing high CPU load and stalling the processing thread for a significant amount of time. In case of ASGI application, this could stall the event loop and prevent other requests from being processed, resulting in a denial of service (DoS). This vulnerability is fixed in 0.0.18.

References

• https://github.com/Kludex/python-multipart/security/advisories/GHSA-59g5-xgcq-4qw3
• https://github.com/Kludex/python-multipart/commit/c4fe4d3cebc08c660e57dd709af1ffa7059b3177