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TI-2026-67612 Aliases CVE-2026-77803GHSA-xq67-hr2w-mm32

Telerik Fiddler Classic front-end desynchronization enables request smuggling

Priority LOW 16CWE-444Published · Updated

Key facts

Attack vector
Local
Privileges required
Low
User interaction
None
Attack complexity
High
Impact type
—
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

In Progress Telerik Fiddler Classic for Windows, versions from 1.0.0 before 6.0.20262.10021, is affected by a front-end request desynchronization flaw in its proxy request forwarding component. A request containing both Content-Length and Transfer-Encoding headers is forwarded with both present, while Fiddler frames the body using Transfer-Encoding only, which is an inconsistent interpretation of HTTP requests (CWE-444). A local attacker with low privileges can split one malformed request into two requests sent to the origin server and receive an additional smuggled response, without needing a vulnerable server.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00097 0th percentileScored 2026-11-07
Fix Fixed Progress® Telerik® Fiddler® Classic (Progress Software): 6.0.20262.10021

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
ProgressProgress® Telerik® Fiddler® Classic1.0.0 to before 6.0.20262.100216.0.20262.10021Patch availableCNA
  • Progress® Telerik® Fiddler® Classic VendorProgress Affected 1.0.0 to before 6.0.20262.10021 Fixed in 6.0.20262.10021 Patch available CNA

Remediation

Update Progress Telerik Fiddler Classic for Windows to version 6.0.20262.10021 or later.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

  • Fix · CNA Progress® Telerik® Fiddler® Classic (Progress Software) Fixed in 6.0.20262.10021

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    Progress® Telerik® Fiddler® Classic 6.0.20262.10021

    4 records Highest priority Priority LOW 4 LOW

    Other records, highest priority first

    • TI-2026-67614 Weak helper tool signature checks in Telerik Fiddler ClassicPriority LOW 35
    • TI-2026-67613 Race condition in Progress Telerik Fiddler Classic certificate installationPriority LOW 30
    • TI-2026-67611 HTTP request smuggling in Progress Telerik Fiddler ClassicPriority LOW 29
    Show all 4 records →

Timeline

  1. 2026-10-05 Threatist record created from CVE-2026-77803
  2. 2026-10-05 Alias added: GHSA-xq67-hr2w-mm32
  3. 2026-10-06 CISA SSVC decision points changed

References

Advisory 1

  • TI-2026-07083 Command injection in Progress LoadMaster KEVCVSS 3.1CRITICAL 9.8
  • TI-2024-06182 WhatsUp Gold HasErrors SQL Injection Authentication Bypass Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2024-04541 WhatsUp Gold GetFileWithoutZip Directory Traversal Remote Code Execution Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2024-04060 Registration Authentication Bypass Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2024-01127 LoadMaster Pre-Authenticated OS Command Injection KEVCVSS 3.1CRITICAL 10.0
  • TI-2023-20934 WS_FTP Server Ad Hoc Transfer Module .NET Deserialization Vulnerability KEVCVSS 3.1CRITICAL 10.0
See all 436 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences