CVE-2026-53538

{
  "id": "CVE-2026-53538",
  "sourceIdentifier": "[email protected]",
  "published": "2026-06-22T18:16:44.223",
  "lastModified": "2026-10-25T23:10:00.167",
  "vulnStatus": "Analyzed",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    },
    {
      "lang": "es",
      "value": "Python-Multipart es un analizador multipart de streaming para Python. Antes de la versión 0.0.30, QuerystringParser trataba el ; como un separador de campos en cuerpos application/x-www-form-urlencoded, además del &. El estándar de URL de WHATWG, los navegadores modernos y urllib.parse de Python (desde la corrección de CVE-2021-23336) tratan solo el & como un separador. Esto crea un diferencial de analizador: los mismos bytes son tokenizados en campos diferentes de los que produciría un intermediario compatible con WHATWG, permitiendo a un atacante introducir de contrabando campos de formulario adicionales más allá de un componente de inspección de cuerpo ascendente. Esta vulnerabilidad está corregida en la versión 0.0.30."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "Kludex",
          "product": "python-multipart",
          "versions": [
            {
              "version": "< 0.0.30",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
          "baseScore": 3.7,
          "baseSeverity": "LOW",
          "attackVector": "NETWORK",
          "attackComplexity": "HIGH",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "LOW",
          "availabilityImpact": "NONE"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 1.4
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-06-23T14:49:11.715345Z",
          "id": "CVE-2026-53538",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-436"
        },
        {
          "lang": "en",
          "value": "CWE-444"
        }
      ]
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "operator": "OR",
          "negate": false,
          "cpeMatch": [
            {
              "vulnerable": true,
              "criteria": "cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*",
              "versionEndExcluding": "0.0.30",
              "matchCriteriaId": "381A8F1D-278D-409F-974A-898BE65DB20C"
            }
          ]
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-6jv3-5f52-599m",
      "source": "[email protected]",
      "tags": [
        "Vendor Advisory"
      ]
    }
  ]
}