{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-77803",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-06T17:50:20.748709Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-06T17:50:34.935Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "platforms": [
            "Windows"
          ],
          "product": "Progress\u00ae Telerik\u00ae Fiddler\u00ae Classic",
          "vendor": "Progress Software",
          "versions": [
            {
              "lessThan": "6.0.20262.10021",
              "status": "affected",
              "version": "1.0.0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "NATO Cyber Security Centre (NCSC)"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "In Progress\u00ae Telerik\u00ae Fiddler\u00ae 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."
            }
          ],
          "value": "In Progress\u00ae Telerik\u00ae Fiddler\u00ae 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."
        }
      ],
      "impacts": [
        {
          "capecId": "CAPEC-33",
          "descriptions": [
            {
              "lang": "en",
              "value": "CAPEC-33 HTTP Request Smuggling"
            }
          ]
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "LOCAL",
            "availabilityImpact": "NONE",
            "baseScore": 3.6,
            "baseSeverity": "LOW",
            "confidentialityImpact": "LOW",
            "integrityImpact": "LOW",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-444",
              "description": "CWE-444: Inconsistent Interpretation of HTTP Requests (\u0027HTTP Request/Response Smuggling\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-05T12:39:36.806Z",
        "orgId": "f9fea0b6-671e-4eea-8fde-31911902ae05",
        "shortName": "ProgressSoftware"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://docs.telerik.com/fiddler/knowledge-base/kb-security-front-end-desynchronization-cve-2026-77803"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "Front-end Desynchronization Vulnerability in Progress\u00ae Telerik\u00ae Fiddler\u00ae Classic",
      "workarounds": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cdiv\u003eDisable client connection reuse in Fiddler Classic: open \u003cb\u003eTools \u0026gt; Options \u0026gt; Connections\u003c/b\u003e and uncheck the \u003cb\u003e\"Reuse client connections\"\u003c/b\u003e checkbox. Disabling client pipe reuse prevents the excess data of a malformed request from being parsed as a pipelined request.\u003c/div\u003e"
            }
          ],
          "value": "Disable client connection reuse in Fiddler Classic: open Tools \u003e Options \u003e Connections and uncheck the \"Reuse client connections\" checkbox. Disabling client pipe reuse prevents the excess data of a malformed request from being parsed as a pipelined request."
        }
      ],
      "x_generator": {
        "engine": "Vulnogram 0.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "f9fea0b6-671e-4eea-8fde-31911902ae05",
    "assignerShortName": "ProgressSoftware",
    "cveId": "CVE-2026-77803",
    "datePublished": "2026-10-05T12:39:36.806Z",
    "dateReserved": "2026-08-21T13:37:32.974Z",
    "dateUpdated": "2026-10-06T17:50:34.935Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}