CVE-2026-77805
Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® Classic
- Published
- Updated
- Reserved
- Assigned by
- ProgressSoftware
Description
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, the integrity check applied to the external helper tools launched by the application is insufficient. Before executing a helper tool, the application only verifies that the file carries a valid Authenticode signature whose certificate subject name matches a broad allow list of publisher name fragments, rather than verifying that the file is the specific executable shipped with that version of the product. A local threat actor with low privileges who replaces one of these helper executables with any other validly signed binary from an allow-listed publisher can cause the substituted binary to be executed by the application, including with Administrator privileges for the tools that request elevation, resulting in privilege escalation and execution of unintended code. Successful exploitation requires the user to launch the affected external tool and to approve the elevation prompt without noticing that it refers to a different executable.
Timeline
ID reserved
By ProgressSoftware
- 45 days later
· 45 days later
Published
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 | High7.9 | CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N |
| NVDNVD · Awaiting Analysis | 3.1 | High7.9 | CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N |
- EPSS (exploitation in 30 days)
- 0.07% · top 100% of all CVEs (7 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: High 7.9.
Weakness
Affected products
Progress Software · Progress® Telerik® Fiddler® Classic
- affected 1.0.0 – < 6.0.20262.10021
What to do
Workaround: Carefully review every User Account Control elevation prompt raised by Fiddler Classic and confirm that it refers to the expected executable before approving it. Alternatively, avoid launching external tools from the Fiddler Classic application, such as the Windows 8 Loopback Exemptions tool or the machine store certificate trust tool.
References (1)
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)
- 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://trackcve.app/cve/CVE-2026-77805)Record last updated .