Python-Multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service_CVE-2026-53539

{
    "lastseen": "",
    "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.",
    "published": "2026-06-22T16:55:42.787Z",
    "modified": "2026-06-22T16:55:42.787Z",
    "type": "cve",
    "title": "Python-Multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service",
    "source": "GitHub_M",
    "references": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-5rvq-cxj2-64vf",
    "id": "CVE-2026-53539",
    "bulletinFamily": "",
    "cwe": [
        "CWE-400",
        "CWE-407"
    ],
    "cvelist": null,
    "sourceData": "Kludex python-multipart < 0.0.30",
    "sourceHref": "",
    "cvss": {
        "score": 7.5,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
        "version": "3.1"
    },
    "cvss2": [],
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        "baseScore": 0,
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        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
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    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "python-multipart",
    "version": "< 0.0.30",
    "vendor": "Kludex",
    "ai_description": "",
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    "ai_score": 0
}