Race Condition Vulnerability in Telerik Fiddler Classic for Windows

CVE-2026-77804

What is CVE-2026-77804?

A time-of-check time-of-use (TOCTOU) race condition affects Telerik Fiddler Classic for Windows, allowing a local threat actor with low privileges to manipulate the installation of an HTTPS interception root certificate into the Local Computer certificate store. This vulnerability arises when Fiddler writes the certificate to a temporary file in a user-writable location and subsequently initiates the external TrustCert helper application to elevate permissions and import the certificate. If an attacker replaces the temporary file before the helper reads it, they can introduce a malicious root certificate into the Local Computer Trusted Root Certification Authorities store. This facilitates the interception and modification of TLS-protected traffic, provided the user triggers the certificate trust operation and approves the elevation prompt.

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