{"cve":"CVE-2026-53539","nvd":{"published":"2026-06-22T18:16:44.360","modified":"2026-10-25T23:10:00.167","status":"Analyzed","description":"Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. 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:N/A:H","score":7.5},"cwes":["CWE-400","CWE-407"],"references":["https://github.com/Kludex/python-multipart/security/advisories/GHSA-5rvq-cxj2-64vf"],"products":["fastapiexpert:python-multipart"],"source":"nvd","synced_at":"2026-10-25T23:44:33.281319194+00:00"},"epss":{"cve":"CVE-2026-53539","score":0.0046,"percentile":0.39614,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-5rvq-cxj2-64vf","url":"https://osv.dev/vulnerability/GHSA-5rvq-cxj2-64vf","summary":"python-multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service","modified":"2026-09-10T03:50:48.426087467Z","packages":[{"ecosystem":"PyPI","name":"python-multipart","purl":"pkg:pypi/python-multipart","ranges":["<0.0.30"],"fixed":["0.0.30"]}]},{"id":"PYSEC-2026-3036","url":"https://osv.dev/vulnerability/PYSEC-2026-3036","summary":"python-multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service","modified":"2026-07-13T16:33:29.036422056Z","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."]}