CVE-2026-86158

Missing authentication in the local .NET backend (Fiddler.WebUi) of Progress Software Fiddler…

Risk score: 56/100
CVSS: 7.7 v3.1
Exploit chance (30 days): 0.1%
Published: 29 Sep 2026

Open in the live forecast Today's forecast

What to know

What it is: 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.
Affected: See advisory
Fix: Apply the vendor's security update; see the linked advisory.
Exploitation: No known exploitation

Why it is Yellow

CVSS 7.7 high
On your watchlist: .net

References

https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-authentication-for-critical-function-cve-2026-86158

Original 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.

Last activity 29 Sep 2026. Patch Forecast updates every hour.