{"id":"PYSEC-2026-1851","summary":"Denial of service (DoS) via deformation `multipart/form-data` boundary","details":"### Summary\n\nWhen 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.\n\nAn 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).\n\n### Impact\n\nApplications that use `python-multipart` to parse form data (or use frameworks that do so) are affected. \n\n### Original Report\n\nThis security issue was reported by:\n- GitHub security advisory in Starlette on October 30 by @Startr4ck\n- Email to `python-multipart` maintainer on October 3 by @mnqazi","aliases":["CVE-2024-53981","GHSA-59g5-xgcq-4qw3"],"modified":"2026-07-07T17:48:07.212662534Z","published":"2026-07-07T14:34:46.120148Z","references":[{"type":"WEB","url":"https://github.com/Kludex/python-multipart/security/advisories/GHSA-59g5-xgcq-4qw3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-53981"},{"type":"WEB","url":"https://github.com/Kludex/python-multipart/commit/c4fe4d3cebc08c660e57dd709af1ffa7059b3177"},{"type":"PACKAGE","url":"https://github.com/Kludex/python-multipart"},{"type":"PACKAGE","url":"https://pypi.org/project/python-multipart"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-59g5-xgcq-4qw3"}],"affected":[{"package":{"name":"python-multipart","ecosystem":"PyPI","purl":"pkg:pypi/python-multipart"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.18"}]}],"versions":["0.0.1","0.0.10","0.0.11","0.0.12","0.0.13","0.0.14","0.0.15","0.0.16","0.0.17","0.0.2","0.0.3","0.0.4","0.0.5","0.0.6","0.0.7","0.0.8","0.0.9"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/python-multipart/PYSEC-2026-1851.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}