{"cve":"CVE-2026-53538","nvd":{"published":"2026-06-22T18:16:44.223","modified":"2026-10-25T23:10:00.167","status":"Analyzed","description":"Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, QuerystringParser treated ; as a field separator in application/x-www-form-urlencoded bodies, in addition to &. The WHATWG URL standard, modern browsers, and Python's urllib.parse (since the CVE-2021-23336 fix) treat only & as a separator. This creates a parser differential: the same bytes are tokenized into different fields than a WHATWG compliant intermediary would produce, allowing an attacker to smuggle extra form fields past an upstream body inspecting component. This vulnerability is fixed in 0.0.30.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","score":3.7},"cwes":["CWE-436","CWE-444"],"references":["https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m"],"products":["fastapiexpert:python-multipart"],"source":"nvd","synced_at":"2026-10-25T23:44:33.281319194+00:00"},"epss":{"cve":"CVE-2026-53538","score":0.00256,"percentile":0.1701,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-6jv3-5f52-599m","url":"https://osv.dev/vulnerability/GHSA-6jv3-5f52-599m","summary":"python-multipart: Semicolon treated as querystring field separator enables parameter smuggling","modified":"2026-09-10T03:51:07.925895532Z","packages":[{"ecosystem":"PyPI","name":"python-multipart","purl":"pkg:pypi/python-multipart","ranges":["<0.0.30"],"fixed":["0.0.30"]}]},{"id":"PYSEC-2026-3037","url":"https://osv.dev/vulnerability/PYSEC-2026-3037","summary":"python-multipart: Semicolon treated as querystring field separator enables parameter smuggling","modified":"2026-07-13T16:33:29.021693741Z","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."]}