CVE-2026-77803

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 v3 3.6 LOW

3.6^/10

CVSS v3 : LOW

Vector :

Exploitability : 1.0 / Impact : 2.5

Attack Vector LOCAL

Attack Complexity HIGH

Privileges Required LOW

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://docs.telerik.com/fiddler/knowledge-base/kb-security-front-end-desynchronization-cve-2026-77803

Configurations

No configuration.

History

05 Oct 2026, 13:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-05 13:16

Updated : 2026-10-06 18:16

NVD link : CVE-2026-77803

Mitre link : CVE-2026-77803

CVE.ORG link : CVE-2026-77803

JSON object : View

Products Affected

No product.

CWE

CWE-444

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

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