High · CVSS 7.9CVE-2026-77805

Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® ClassicCVE-2026-77805

Answer in brief

CVE-2026-77805 records a High severity (CVSS 7.9) vulnerability in Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® Classic. The current sources do not mark it as known exploited. The current feed maps Progress Software/Progress® Telerik® Fiddler® Classic (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 5, 2026Updated Oct 5, 2026Source checked Oct 5, 2026First seen by HOL Oct 5, 2026Material review Oct 5, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.9
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 7.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Progress Software/Progress® Telerik® Fiddler® Classic (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Progress Software/Progress® Telerik® Fiddler® Classicgeneric	>=1.0.0 <6.0.20262.10021	6.0.20262.10021

Recommended response

Check inventory. Check lockfiles and deployed manifests for Progress Software/Progress® Telerik® Fiddler® Classic.
Review the reported fix. Source-reported workaround: 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.

Evidence timeline and material changes

Published upstream
Oct 5, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 5, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 5, 2026

Sources and claim methodology

Source referencedocs.telerik.com

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.