CVE-2026-77804 Race condition in Progress® Telerik® Fiddler® Classic
A local attacker can exploit a race condition during root certificate installation to inject a malicious certificate, enabling TLS traffic interception and modification.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-77804?
CVE-2026-77804 is a medium-severity vulnerability in Progress® Telerik® Fiddler® Classic, published on 5 Oct 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, a time-of-check time-of-use (TOCTOU) race condition exists in the installation of the HTTPS interception root certificate into the Local Computer certificate store. Fiddler writes the certificate to a temporary file in a user-writable location and then launches the external TrustCert helper application, which elevates and imports the certificate from that file. A local threat actor with low privileges who replaces the temporary file between the time it is written and the time the elevated helper reads it can cause an attacker-supplied root certificate to be installed in the Local Computer Trusted Root Certification Authorities store, enabling subsequent interception and modification of TLS-protected traffic on the machine. Successful exploitation requires the user to initiate the certificate trust operation and approve the elevation prompt.
Weakness: CWE-367
Which versions are affected by CVE-2026-77804?
How do I fix CVE-2026-77804?
No fix has been published for CVE-2026-77804 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-77804 being exploited?
There is no known exploitation of CVE-2026-77804 in the wild and no public exploit code.
Sources
Also known as GHSA-rx7m-qprj-p54h.