{"id":"CVE-2026-53537","summary":"Python-Multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters","details":"Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, parse_options_header parsed Content-Disposition (and Content-Type) headers with email.message.Message, which transparently applies RFC 2231/5987 decoding. The extended parameter syntax (filename*=charset'lang'value, name*=..., and the filename*0/filename*1 continuation form) is decoded and surfaced under the bare filename/name key, and overrides the plain parameter when both are present. RFC 7578 §4.2 explicitly forbids the filename* form in multipart/form-data. Components that follow RFC 7578, or that do not implement RFC 2231/5987 decoding for multipart/form-data (WAFs, proxies, gateways), may interpret such a header differently. An attacker can exploit that difference to smuggle a different field name or filename past an upstream inspector to the backend. This vulnerability is fixed in 0.0.30.","aliases":["GHSA-vffw-93wf-4j4q"],"modified":"2026-07-08T08:13:43.925344844Z","published":"2026-06-22T16:57:21.496Z","related":["CGA-x9x2-h6wq-m4f8","SUSE-SU-2026:22372-1","openSUSE-SU-2026:11099-1","openSUSE-SU-2026:21066-1"],"database_specific":{"cwe_ids":["CWE-20","CWE-436"],"cna_assigner":"GitHub_M","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53537.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53537.json"},{"type":"ADVISORY","url":"https://github.com/Kludex/python-multipart/security/advisories/GHSA-vffw-93wf-4j4q"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-53537"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/kludex/python-multipart","events":[{"introduced":"0"},{"fixed":"9d3ead568a259f222cff6425262ff63e88d930d4"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"0.0.30"}],"source":["AFFECTED_FIELD","CPE_RANGE"],"cpe":"cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*"}}],"versions":["0.0.29","0.0.28","0.0.27","0.0.26","0.0.25","0.0.24","0.0.23","0.0.22","0.0.21","0.0.20","0.0.19","0.0.18","0.0.17","0.0.16","0.0.15","0.0.14","0.0.13","0.0.12","0.0.11","0.0.10","0.0.9","0.0.8","0.0.7","0.0.6","0.0.5","0.0.4","0.0.2"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53537.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"}]}