{"cve":"CVE-2026-53537","nvd":{"published":"2026-06-22T18:16:44.077","modified":"2026-10-25T23:10:00.167","status":"Analyzed","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","score":5.3},"cwes":["CWE-20","CWE-436"],"references":["https://github.com/Kludex/python-multipart/security/advisories/GHSA-vffw-93wf-4j4q"],"products":["fastapiexpert:python-multipart"],"source":"nvd","synced_at":"2026-10-25T23:44:33.281319194+00:00"},"epss":{"cve":"CVE-2026-53537","score":0.00291,"percentile":0.21505,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-vffw-93wf-4j4q","url":"https://osv.dev/vulnerability/GHSA-vffw-93wf-4j4q","summary":"python-multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters","modified":"2026-09-10T03:50:50.585695996Z","packages":[{"ecosystem":"PyPI","name":"python-multipart","purl":"pkg:pypi/python-multipart","ranges":["<0.0.30"],"fixed":["0.0.30"]}]},{"id":"PYSEC-2026-3041","url":"https://osv.dev/vulnerability/PYSEC-2026-3041","summary":"python-multipart: Content-Disposition parameter smuggling via RFC 2231/5987 extended parameters","modified":"2026-07-13T16:33:29.205974608Z","packages":[{"ecosystem":"PyPI","name":"python-multipart","purl":"pkg:pypi/python-multipart","ranges":["<0.0.30"],"fixed":["0.0.30"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}