CVE-2026-77803
Front-end Desynchronization Vulnerability in Progress® Telerik® Fiddler® Classic
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.
| CWE | CWE-444 |
| Vendor | progress software |
| Product | progress® telerik® fiddler® classic |
| Published | Oct 5, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N