CVE-2026-77804Time-of-check Time-of-use (TOCTOU) Race Condition in Root Certificate Installation in Progress® Telerik® Fiddler® Classic
- 6.6MediumCVSS base score
- 0.07%Exploitation in 30 daysEPSS · top 100% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
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.
Timeline
ID reserved
By ProgressSoftware
- 45 days later
· 45 days later
Published
- 1 day later
· 1 day later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| ProgressSoftwareCNA (assigner) | 3.1 | Medium6.6 | CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N |
| NVDNVD · Awaiting Analysis | 3.1 | Medium6.6 | CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N |
- EPSS (exploitation in 30 days)
- 0.07% · top 100% of all CVEs (12 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.6.
Affected products
Progress Software · Progress® Telerik® Fiddler® Classic
- affected 1.0.0 – < 6.0.20262.10021
What to do
Workaround: Trust the Fiddler Classic certificate only in the Current User certificate store. When the application asks to install the certificate in the Local Computer (local machine) store, choose No. If a machine-wide trust is required, export the certificate to a file and import that file into the Local Computer Trusted Root Certification Authorities store manually.
References
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-92427 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-77804)Record last updated .