Missing Authentication in the local .NET backend of Progress Telerik Fiddler Everywhere

published 2026-09-29 41 d ago modified 2026-09-30 39 d ago also EUVD-2026-88649

cvss: 7.7; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 0%
public exploits: 0; none known

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.

Patch / fix

fixed in 1

Progress Software Progress® Telerik® Fiddler® Everywhere 8.2.0

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 39 d ago (2026-09-30)

Exploit prediction

0.09% chance of exploitation in the next 30 days, higher than 0% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.7	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Progress Software Progress® Telerik® Fiddler® Everywhere

Classification

Weakness

CWE-306 Missing Authentication for Critical Functionality

References

telerik.com /fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-authentication-for-critical-funct
vendor-advisory

Sources

CVE List CVE-2026-86158
NVD CVE-2026-86158

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary