CVE-2026-86158

High

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.

SeverityHigh

CVSS7.7

Exploit probability—

ProductProgress® Telerik® Fiddler® Everywhere

PublishedSep 29, 2026

First seenSep 29, 2026

Weakness typeCWE-306Missing authentication for critical function

How to fix

Update

Progress Software Progress® Telerik® Fiddler® Everywhere8.2.0 or later

Vendor advisories

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

Affected products

Product	Affected versions	Fixed in
Progress Software Progress® Telerik® Fiddler® Everywhere	1.0.0 ≤ v < 8.2.0	8.2.0

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