Unauthenticated Local Access to OAuth Tokens and Certificates

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.

Casky was already ahead

This CVE exploits attack patterns that Casky's 283matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2026-86158 exposes a critical authentication bypass in Progress Fiddler Everywhere 8.0.2, where the local .NET backend (Fiddler.WebUi) fails to implement proper authentication mechanisms on its localhost HTTP and SignalR RPC channels. This vulnerability allows any local, unauthenticated attacker to mint OAuth tokens and extract the machine-in-the-middle root certificate—two highly sensitive assets that undermine both authentication integrity and encrypted communications. Organizations relying on Fiddler Everywhere for traffic analysis, debugging, or security testing face immediate risk, as compromise of OAuth tokens enables lateral movement and impersonation, while root certificate theft facilitates persistent man-in-the-middle attacks across an organization's infrastructure.

Casky's 283 matching skills leverage Claude's extended reasoning to map this vulnerability across MITRE ATT&CK Privilege Escalation (TA0004) and Credential Access (TA0006) techniques. Security practitioners using the platform would detect attack patterns including: unauthorized token generation indicative of TA0004 exploitation attempts; suspicious unauthenticated RPC channel activity pointing to missing authentication enforcement; and lateral movement indicators following credential compromise. The skills enable practitioners to correlate localhost HTTP access logs, SignalR connection anomalies, and certificate store modifications—revealing when attackers exploit this local bypass to establish persistence or move laterally across network segments. This multi-layered detection approach transforms raw vulnerability intelligence into actionable threat hunting and containment guidance.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

283 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-86158.

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

Access with Stolen Session Cookie

identity access management · low

Run

MITRE ATT&CK Techniques

TA0004 TA0006

Investigate the attack patterns behind CVE-2026-86158

Casky has 283 skills that investigate the attack patterns behind CVE-2026-86158. Run one and get CVSS-scored findings in 3 minutes.

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