Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling_CVE-2026-53538

{
    "lastseen": "",
    "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.",
    "published": "2026-06-22T16:56:32.628Z",
    "modified": "2026-06-22T16:56:32.628Z",
    "type": "cve",
    "title": "Python-Multipart: Semicolon treated as querystring field separator enables parameter smuggling",
    "source": "GitHub_M",
    "references": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m",
    "id": "CVE-2026-53538",
    "bulletinFamily": "",
    "cwe": [
        "CWE-436",
        "CWE-444"
    ],
    "cvelist": null,
    "sourceData": "Kludex python-multipart < 0.0.30",
    "sourceHref": "",
    "cvss": {
        "score": 3.7,
        "severity": "LOW",
        "vector": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
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        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
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        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
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            "baseScore": 0,
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "python-multipart",
    "version": "< 0.0.30",
    "vendor": "Kludex",
    "ai_description": "",
    "ai_severity": "",
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    "ai_score": 0
}