CVE-2026-77804

MEDIUMPre-NVD 6.66.6—
EchelonGraph scoreHIGH confidence

Score 6.6 from GitHub Security Advisory published 2026-10-05. A secondary CVSS source baseline 6.6; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
6.6EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: <0.1%CVSS: 6.6Exploit: None knownExposed services: Not assessed

No fix is confirmed yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for the fix.

In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, a time-of-check time-of-use (TOCTOU) race condition exists in the installation of the HTTPS interception root certificate into the Local Computer certificate store. Fiddler writes the certificate to a temporary file in a user-writable location and then launches the external TrustCert helper application, which elevates and imports the certificate from that file. A local threat actor with low privileges who replaces the temporary file between the time it is written and the time the elevated helper reads it can cause an attacker-supplied root certificate to be installed in the Local Computer Trusted Root Certification Authorities store, enabling subsequent interception and modification of TLS-protected traffic on the machine. Successful exploitation requires the user to initiate the certificate trust operation and approve the elevation prompt.

CVSS v3
6.6
EG Score
6.6MEDIUMhigh confidence
EG Risk
30
EG Risk 30/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity66% × 45%
Exploitation0% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines, and watch the vendor's advisory for the fix.
EPSS PROB
<0.1%
EPSS %ILE
below the 1st
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* at high (mission-essential systems).

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines, and watch the vendor's advisory for the fix.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

October 5, 2026

Last Modified

October 6, 2026

Advisory Details (1)

Auto-updated Oct 5, 2026
No fix on record yet.
generic

Fiddler Classic Time-of-check Time-of-use (TOCTOU) Race Condition in Root Certificate Installation Vulnerability (CVE-2026-77804) - Progress Telerik Fiddler Classic

https://docs.telerik.com/fiddler/knowledge-base/kb-security-root-certificate-installation-toctou-cve-2026-77804

Vendor Advisories for CVE-2026-77804(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 13× in last 7d / 13× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-10-07 16:22 UTCGHSA enrichment
  2. 2026-10-06 18:33 UTCEG score recompute
  3. 2026-10-06 18:33 UTCGHSA enrichment
  4. 2026-10-06 17:57 UTCEG score recompute
  5. 2026-10-06 17:57 UTCGHSA enrichment
  6. 2026-10-06 15:25 UTCEG score recompute
  7. 2026-10-06 15:25 UTCGHSA enrichment
  8. 2026-10-06 15:18 UTCEPSS rescore
  9. 2026-10-06 11:00 UTCEG score recompute
  10. 2026-10-06 11:00 UTCGHSA enrichment
  11. 2026-10-05 13:18 UTCEG score recompute
  12. 2026-10-05 13:02 UTCEG score recompute
  13. 2026-10-05 13:01 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-77804?
CVE-2026-77804 is a medium vulnerability published on October 5, 2026. In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, a time-of-check time-of-use (TOCTOU) race condition exists in the installation of the HTTPS interception root certificate into the Local Computer certificate store. Fiddler writes the certificate to a temporary…
When was CVE-2026-77804 disclosed?
CVE-2026-77804 was first published on October 5, 2026, with the most recent update on October 6, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-77804 actively exploited?
CVE-2026-77804 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a <0.1% probability of exploitation in the next 30 days (below the 1st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-77804?
CVE-2026-77804 has a CVSS base score of 6.6 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-77804?
No fix for CVE-2026-77804 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The vendor advisories EchelonGraph has for CVE-2026-77804 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-77804

Explore →

Is Your Infrastructure Affected by CVE-2026-77804?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Book a Demo →Browse All CVEs