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CVE-2026-77803

Estado: Pendiente de análisisBaja (3.6)—

In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, front-end request desynchronization is possible in the proxy request forwarding component. A request that contains both a Content-Length and a Transfer-Encoding header is forwarded with both headers present, while Fiddler frames the body using Transfer-Encoding only. The remaining bytes on the reused client connection are then parsed as a separate pipelined request, so a local threat actor with low privileges can cause a single malformed request to be split into two requests forwarded to the origin server and receive an additional smuggled response, without requiring a vulnerable server.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

AV:L/PR:L/UI:N indica escalada local. HTTP request smuggling (CWE-444) permite al atacante interceptar/manipular tráfico de red (MITM) y potencialmente corromper datos en tránsito mediante desincronización de requests en el componente proxy.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Encrypt Sensitive InformationUser TrainingThreat Intelligence ProgramNetwork SegmentationNetwork Intrusion PreventionLimit Access to Resource Over Network

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Progress — Telerik Fiddler ClassicAI

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-77803",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-77803",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-10-06T17:50:20.748709Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "security@progress.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 3.6,
          "attackVector": "LOCAL",
          "baseSeverity": "LOW",
          "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "NONE",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 2.5,
        "exploitabilityScore": 1
      }
    ]
  },
  "affected": [
    {
      "source": "security@progress.com",
      "affectedData": [
        {
          "vendor": "Progress Software",
          "product": "Progress® Telerik® Fiddler® Classic",
          "versions": [
            {
              "status": "affected",
              "version": "1.0.0",
              "lessThan": "6.0.20262.10021",
              "versionType": "custom"
            }
          ],
          "platforms": [
            "Windows"
          ],
          "defaultStatus": "unaffected"
        }
      ]
    }
  ],
  "published": "2026-10-05T13:16:54.453",
  "references": [
    {
      "url": "https://docs.telerik.com/fiddler/knowledge-base/kb-security-front-end-desynchronization-cve-2026-77803",
      "source": "security@progress.com"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "security@progress.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-444"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, front-end request desynchronization is possible in the proxy request forwarding component. A request that contains both a Content-Length and a Transfer-Encoding header is forwarded with both headers present, while Fiddler frames the body using Transfer-Encoding only. The remaining bytes on the reused client connection are then parsed as a separate pipelined request, so a local threat actor with low privileges can cause a single malformed request to be split into two requests forwarded to the origin server and receive an additional smuggled response, without requiring a vulnerable server."
    }
  ],
  "lastModified": "2026-10-06T18:16:56.270",
  "sourceIdentifier": "security@progress.com"
}