---
title: "CVE-2026-86158: Progress Software Fiddler Everywhere - Authentication Bypass"
description: "Progress Software Fiddler Everywhere 8.0.2 contains a broken authentication caused by missing authentication in the local .NET backend (Fiddler.WebUi), letting local unauthenticated attackers mint OAuth tokens and read the machine-in-the-middle root certificate through localhost HTTP and SignalR RPC channels."
url: https://panop.io/threat-heartbeat/CVE-2026-86158/
---

# CVE-2026-86158 Progress Software Fiddler Everywhere - Authentication Bypass

Progress Software Fiddler Everywhere 8.0.2 contains a broken authentication caused by missing authentication in the local .NET backend (Fiddler.WebUi), letting local unauthenticated attackers mint OAuth tokens and read the machine-in-the-middle root certificate through localhost HTTP and SignalR RPC channels.

CVSS base score 7.7 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.09% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-86158)

## Details

Type

Authentication Bypass

Impact

Information Disclosure, Broken Authentication

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Published

29 September 2026

Updated

15 October 2026

Weakness

[CWE-306](https://cwe.mitre.org/data/definitions/306.html)

## Vendor fix

Update to the latest version of Progress Software Fiddler Everywhere.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-86158](https://nvd.nist.gov/vuln/detail/CVE-2026-86158)
- [https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-exposed-dangerous-method-or-function-cve-2026-aaaaa](https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-exposed-dangerous-method-or-function-cve-2026-aaaaa)
- [https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-authentication-for-critical-function-cve-2026-86158](https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-authentication-for-critical-function-cve-2026-86158)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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