CVE-2026-53539

{
  "id": "CVE-2026-53539",
  "sourceIdentifier": "[email protected]",
  "published": "2026-06-22T18:16:44.360",
  "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, 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."
    },
    {
      "lang": "es",
      "value": "Python-Multipart es un analizador multipart de streaming para Python. Antes de la versión 0.0.30, al analizar cuerpos application/x-www-form-urlencoded, QuerystringParser localizaba el separador de campo con una búsqueda en dos pasos: primero escaneaba todo el búfer restante en busca de &, y solo cuando no existía ningún & más adelante, recurría a escanear en busca de ;. Para un cuerpo que usa ; como separador y no contiene ningún &, cada iteración de campo realizaba un escaneo completo fallido de & sobre todo el búfer restante antes de localizar el ; cercano. Con N campos separados por punto y coma en un fragmento de tamaño B, esto produce O(B^2) comparaciones de bytes por fragmento. Un atacante puede enviar un cuerpo pequeño y manipulado de la forma a;a;a;... y hacer que el analizador gaste segundos de CPU por solicitud. Un puñado de solicitudes concurrentes puede agotar los procesos de trabajo. 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:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-06-23T14:05:50.901666Z",
          "id": "CVE-2026-53539",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-400"
        },
        {
          "lang": "en",
          "value": "CWE-407"
        }
      ]
    }
  ],
  "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-5rvq-cxj2-64vf",
      "source": "[email protected]",
      "tags": [
        "Vendor Advisory"
      ]
    }
  ]
}