CVE-2026-77803 (GCVE-0-2026-77803)

Vulnerability from cvelistv5 – Published: 2026-10-05 12:39 – Updated: 2026-10-06 17:50
VLAI
Title
Front-end Desynchronization Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
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.
Severity
3.6 (Low)
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:50 UTC
CWE
  • CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
Impacted products
Vendor Product Version CPE status
Progress Software Progress® Telerik® Fiddler® Classic Affected: 1.0.0 , < 6.0.20262.10021 (custom)
guessed Create a notification for this product.
Credits
NATO Cyber Security Centre (NCSC)
Show details on NVD website
To clipboard 

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