Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® Classic

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77805
StatePUBLISHED
AssignerProgressSoftware
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-05 13:16:54 UTC
Updated2026-10-06 15:09:20 UTC
DescriptionIn Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, the integrity check applied to the external helper tools launched by the application is insufficient. Before executing a helper tool, the application only verifies that the file carries a valid Authenticode signature whose certificate subject name matches a broad allow list of publisher name fragments, rather than verifying that the file is the specific executable shipped with that version of the product. A local threat actor with low privileges who replaces one of these helper executables with any other validly signed binary from an allow-listed publisher can cause the substituted binary to be executed by the application, including with Administrator privileges for the tools that request elevation, resulting in privilege escalation and execution of unintended code. Successful exploitation requires the user to launch the affected external tool and to approve the elevation prompt without noticing that it refers to a different executable.

Risk And Classification

Primary CVSS: v3.1 7.9 HIGH from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

EPSS: 0.000630000 probability, percentile 0.000100000 (date 2026-10-06)

Problem Types: CWE-347 | CWE-347 CWE-347: Improper Verification of Cryptographic Signature

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.9HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
3.1CNACVSS7.9HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Progress Software Progress Telerik Fiddler Classic affected 1.0.0 6.0.20262.10021 custom Windows

References

ReferenceSourceLinkTags
docs.telerik.com/fiddler/knowledge-base/kb-security-weak-executable-signature-... [email protected] docs.telerik.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: NATO Cyber Security Centre (NCSC) (en)

Additional Advisory Data

Workarounds

CNA: Carefully review every User Account Control elevation prompt raised by Fiddler Classic and confirm that it refers to the expected executable before approving it. Alternatively, avoid launching external tools from the Fiddler Classic application, such as the Windows 8 Loopback Exemptions tool or the machine store certificate trust tool.

© CVE.report 2026

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report