What is CVE-2026-86158?

CVE-2026-86158 is a high-severity vulnerability, classified under Missing Authentication for Critical Function. CVSS score: 7.7/10. Published 2026-09-29.

How severe is CVE-2026-86158?

High severity. CVSS v3 base score is 7.7 out of 10.

CVE-2026-86158

CVE-2026-86158

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.

Vulnerability class: Broken Authentication

Published 2026-09-29.

CVSS v3 metric

CVSS v3 base score 7.7 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Weakness classification (CWE)

CWE-306 — Missing Authentication for Critical Function

References

www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-secu… (vendor-advisory)

Frequently asked questions

What is CVE-2026-86158?: CVE-2026-86158 is a high-severity vulnerability, classified under Missing Authentication for Critical Function. CVSS score: 7.7/10. Published 2026-09-29.
How severe is CVE-2026-86158?: High severity. CVSS v3 base score is 7.7 out of 10.