{"schema":"threatline.record/2","record":{"id":"CVE-2026-77803","aliases":[],"summary":"Front-end Desynchronization Vulnerability in Progress® Telerik® Fiddler® Classic","details":"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.","categories":["Unclassified"],"product":"Progress® Telerik® Fiddler® Classic","vendor":"Progress Software","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-77803","source_modified_at":"2026-10-06T17:50:34.935Z","fetched_at":"2026-10-23T18:52:38.922436Z","product":"Progress® Telerik® Fiddler® Classic","vendor":"Progress Software","versions":[{"status":"affected","version":"1.0.0","lessThan":"6.0.20262.10021","versionType":"custom"}],"defaultStatus":"unaffected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-77803","source_modified_at":"2026-10-06T17:50:34.935Z","fetched_at":"2026-10-23T18:52:38.922436Z","package":{"name":"Progress® Telerik® Fiddler® Classic","ecosystem":null},"version":"6.0.20262.10021","basis":"first unaffected version stated in the CVE record"}],"cvss":3.6,"severity":"Low","kev":{"listed":false},"epss":{"probability":0.00087,"percentile":0.00321,"score_date":"2026-10-23"},"published_at":"2026-10-05T12:39:36.806Z","modified_at":"2026-10-06T17:50:34.935Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-77803","fetched_at":"2026-10-23T18:52:38.922436Z","source_modified_at":"2026-10-06T17:50:34.935Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-77803","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://docs.telerik.com/fiddler/knowledge-base/kb-security-front-end-desynchronization-cve-2026-77803","tags":["vendor-advisory"]}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"none","automatable":"no","technical_impact":"partial","assessed_at":"2026-10-06T17:50:20.748709Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":null,"confidence":"unknown","reviewed":false},"change_timestamp":"2026-10-06T17:50:34.935Z","content_hash":"6436ef37467378b37ab3bbc9a6ae43a9b2482c2b629cca10086ebb3bf64d91d7"}}