CVE-2026-104657

Fiddler’s agent setup skill could execute an unverified installer

Progress Software · Fiddler Download & Setup coding-agent skill

First documented disclosure · Review checkpoint

Summary

The agent skill installed a downloaded artifact without checking its integrity against the release information or a platform signature.

Severity and exploitation evidence

High · 7.5/10 · CVSS 3.1. Severity source.

Exploitation not established: The reviewed public disclosures do not report exploitation in the wild.

Exploitation evidence source

Technical severity is not a measure of observed attacks or of risk to your deployment. Attempts, demonstrations, and successful compromise retain the qualifications in the source.

How the weakness works

The affected skill skipped artifact verification. Its macOS installation flow also staged the package at a predictable temporary location.

Conditions required

A user runs an affected skill. An attacker must influence a release component or, on macOS, have local access to the staging area. Elevated installation requires user approval.

Potential impact

Code could run with the installer’s permissions, including root on macOS after approval.

Affected versions and configurations

The vendor identifies unversioned skill copies downloaded before October 5, 2026.

Fix and mitigation status

The current replacement skill in the official Fiddler agent-tools repository verifies downloads and uses secure temporary storage.

Practical next steps

Remove the affected skill and reinstall its replacement from Progress’s official repository. Updating the Fiddler application alone leaves installed skill copies in place.

Operating lesson

Verify the artifact actually opened by the installer and keep its staging location private.

Evidence and limits

The CNA encodes a boundary of 8.3.0 and gives CVSS 3.1 at 7.5. The vendor’s November 6 bulletin calls the skill unversioned and gives CVSS 3.0 at 8.0. Its install-date guidance is specific to the skill.

Sources