CVE-2026-86158 Missing Authentication in the local .NET backend of Progress Telerik Fiddler Everywhere
Local attackers can bypass authentication to mint OAuth tokens and read the MITM root certificate via the unsecured local backend.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-86158?
CVE-2026-86158 is a high-severity missing authorization vulnerability in Progress® Telerik® Fiddler® Everywhere, published on 29 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Missing authentication in the local .NET backend (Fiddler.WebUi) of Progress Software Fiddler Everywhere 8.0.2 allows a local unauthenticated attacker to mint OAuth tokens and read the machine-in-the-middle root certificate through an unauthenticated localhost HTTP and SignalR RPC channel.
Weakness: CWE-306
Which versions are affected by CVE-2026-86158?
How do I fix CVE-2026-86158?
No fix has been published for CVE-2026-86158 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-86158 being exploited?
There is no known exploitation of CVE-2026-86158 in the wild and no public exploit code.
Sources
Also known as GHSA-rx77-7xhh-crpr.