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CVE-2026-77805: Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® Classic
- Severity: high (CVSS 7.9 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.1% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-10-05 · updated 2026-10-06
- Weakness: CWE-347
Description
In 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.
Affected products
- Progress Software Progress® Telerik® Fiddler® Classic: from 1.0.0 before 6.0.20262.10021 — fixed in 6.0.20262.10021
How to fix
Upgrade to a fixed version: Progress Software Progress® Telerik® Fiddler® Classic 6.0.20262.10021. Check the vendor advisory for mitigations.
References
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