---
id: "CVE-2026-104657"
page: "https://infrastack.ai/live/CVE-2026-104657"
kind: "vulnerability"
aliases: ["CVE-2026-104657"]
title: "Fiddler Download & Setup agent skill installs unverified packages, as root on macOS"
severity: "high"
cvss: 7.5
epss: null
exploited: false
status: "open"
category: "ai-tooling"
products: [{"name": "Fiddler Download & Setup Skill", "fixed": ["current copy in telerik/fiddler-agent-tools"], "affected": "copies downloaded before 2026-10-05 (skill is not versioned)", "ecosystem": "vendor"}]
ecosystems: []
tags: ["ai-skills", "ai-tooling", "fiddler", "linux", "macos", "progress", "telerik", "windows"]
not_affected_if: ["current-skill-copy", "manual-install", "skill-not-installed"]
published_at: "2026-11-06T17:17:11+00:00"
first_seen_at: "2026-11-06T17:43:11+00:00"
updated_at: "2026-11-06T17:46:23+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-104657", "first_seen_at": "2026-11-06T17:43:11+00:00"}, {"source": "analyst", "url": "https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657", "first_seen_at": "2026-11-06T17:46:23+00:00", "cites": ["https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657"]}]
exploit_sources: []
---

# Fiddler Download & Setup agent skill installs unverified packages, as root on macOS

Link for people: https://infrastack.ai/live/CVE-2026-104657 (this .md is for agents)

The Fiddler Download and Setup Skill fails to verify the integrity of the release package it fetches on Linux, macOS, and Windows. An attacker who tampers with that package can run their own code when a user runs the skill, and on macOS a local process can swap the staged package for a root-privileged install.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Fiddler Download & Setup Skill affected copies downloaded before 2026-10-05 (skill is not versioned) fixed current copy in telerik/fiddler-agent-tools

## How to check

- Find copies of the fiddler-download-setup skill in your coding agent or tool (skills folder, or a clone of telerik/fiddler-agent-tools). The skill has no version number: any copy downloaded before October 5, 2026 is affected.
- On macOS, an old copy stages the installer at /tmp/FiddlerEverywhere.pkg and installs it with administrator privileges. Look for that path in the skill file.
- Replace it with the current copy from the repository and follow the agent-skill install instructions.
- Workaround from Progress until then: do not run an existing copy; install Fiddler manually from the official source, verify the publisher signature and checksum, and on macOS use a per-user DMG install without admin privileges.

## Fix

Progress fixed the published Fiddler Download & Setup Skill. It is not versioned and does not auto-update, so delete any copy downloaded before October 5, 2026 and reinstall the latest from the official telerik/fiddler-agent-tools repository. Updating Fiddler Everywhere does not replace the skill.

## Timeline

- 2026-11-06T17:43:11+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-104657
- 2026-11-06T17:46:23+00:00 analyst https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657 — Vendor KB read. Attack needs a compromised/influenced release component (network, high complexity) plus user running the skill; macOS local swap of /tmp/FiddlerEverywhere.pkg is a second path. Vendor KB says copies before Oct 5 2026 and unversioned; OpenCVE's '< 8.3.0' disagrees, not used. Vendor CVSS 8.0 vs NVD 7.5. No exploitation or PoC found.

## Documents

- [advisory] Telerik KB: Download of Code Without Integrity Check (CVE-2026-104657) https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657

## From the sources

Missing integrity verification in the Progress Software Fiddler Download and Setup Skill on Linux, macOS, and Windows which allows an attacker to compromise or influence a release component and execute attacker-controlled code when a user runs the skill. On macOS, the skill stages the package at a predictable path and installs it with administrator privileges, which may allow code execution with root privileges after user approval. A local process may also replace the staged macOS package while the skill waits for approval.

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_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_