CVE-2026-77802

In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, HTTP request smuggling is possible in the proxy request forwarding component. Requests containing multiple Content-Length headers with conflicting values are forwarded verbatim to the origin server, while Fiddler frames the request body using only the first Content-Length value. A local threat actor with low privileges who is able to send requests through the same Fiddler proxy instance as another user can exploit this desynchronization against a non-RFC-9110-compliant origin server that keeps the connection alive to smuggle an additional request. Because Fiddler returns the server connection to its pipe pool after reading only the first response, the unread smuggled response remains buffered on the socket and is served to the next session that reuses that connection, allowing the attacker to poison responses delivered to other users and to obtain responses intended for them.

CVSS v3 6.3 MEDIUM

6.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 1.0 / Impact : 5.2

Attack Vector LOCAL

Attack Complexity HIGH

Privileges Required LOW

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://docs.telerik.com/fiddler/knowledge-base/kb-security-http-request-smuggling-cve-2026-77802

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-2026-77802

Mitre link : CVE-2026-77802

CVE.ORG link : CVE-2026-77802

JSON object : View

Products Affected

No product.

CWE

CWE-444

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

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