CVE-2026-77804

Root certificate trust hijack via temporary-file race

Published Oct 5, 2026 · Updated Oct 5, 2026

Certificate trust race in Progress Telerik Fiddler Classic before 6.0.20262.10021 allows local users to install an attacker root CA. During machine-wide trust, Fiddler writes the certificate to a user-writable temporary file that the elevated TrustCert helper subsequently imports without protecting it from replacement. Exploitation requires another user to initiate certificate trust and approve elevation; the installed root can then enable interception or modification of TLS traffic.

CVSS severityUnavailable
Unscored
EPSS probability0.06%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Certificate trust race in Progress Telerik Fiddler Classic before 6.0.20262.10021 allows local users to install an attacker root CA. During machine-wide trust, Fiddler writes the certificate to a user-writable temporary file that the elevated TrustCert helper subsequently imports without protecting it from replacement. Exploitation requires another user to initiate certificate trust and approve elevation; the installed root can then enable interception or modification of TLS traffic.

The record

CVE
CVE-2026-77804
Published
Oct 5, 2026
Updated
Oct 5, 2026
Vendor
Progress Software Corporation
Product
Fiddler Classic
Classifications
T1553.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.0.0 <6.0.20262.10021

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Progress Software Corporation · Fiddler Classicversion=1.0.0 <6.0.20262.10021

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1553.004Subvert Trust Controls: Install Root Certificate

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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