{"id":"CVE-2026-104657","kind":"vulnerability","aliases":["CVE-2026-104657"],"related":[],"title":"Fiddler Download & Setup agent skill installs unverified packages, as root on macOS","description":"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.","summary":"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.","severity":"high","cvss":7.5,"epss":null,"exploited":false,"exploited_at":null,"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"],"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.\n- 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.\n- Replace it with the current copy from the repository and follow the agent-skill install instructions.\n- 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.","status":"open","published_at":"2026-11-06T17:17:11+00:00","first_seen_at":"2026-11-06T17:43:11+00:00","triaged_at":"2026-11-06T17:45:06+00:00","updated_at":"2026-11-06T17:46:23+00:00","category":"ai-tooling","confidence":0.85,"triage":{"at":"2026-11-06T17:45:06Z","model":"claude-haiku-5-5","output":{"fix":"unknown","reach":"local","title":"Fiddler download skill skips integrity checks, runs attacker code on install","impact":"high","summary":"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.","audience":"developers","category":"ai-tooling","nicknames":[],"who_cares":["fiddler","progress","macos","linux","windows","ai-skills"],"confidence":0.5,"fix_status":"unknown","needs_auth":"no","worst_case":"Attacker code runs with root privileges on macOS after user approval","analyst_note":"Find the vendor advisory or fixed skill version for CVE-2026-104657 and confirm the macOS staging path and whether the flaw is local-only or reachable remotely.","how_to_check":"- Check whether the Fiddler Download and Setup Skill is installed on the machine, in the agent or tool that loads it.\n- On macOS, check whether the skill stages packages at a predictable path before its administrator install step.\n- Note the installed skill version and compare it with the fixed version, which the sources do not state.","plain_action":"","needs_analyst":true,"not_affected_if":["skill-not-installed"],"who_is_affected":"Teams that run the Progress Fiddler Download and Setup Skill on Linux, macOS, or Windows, especially on macOS where the skill installs with administrator privileges. Teams that do not use this skill are not affected. The sources do not say which skill versions are vulnerable.","user_interaction":"yes","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000731,"input_tokens":4277,"output_tokens":607,"severity_before":"high"},"analyst_status":"done","analyst_note":"Find the vendor advisory or fixed skill version for CVE-2026-104657 and confirm the macOS staging path and whether the flaw is local-only or reachable remotely.","search":"'-104657':15A,18A '-2026':14A,17A 'administr':147C 'agent':4A 'ai':24B,27B 'ai-skil':23B 'ai-tool':26B 'allow':110C,151C 'also':164C 'approv':159C,175C 'attack':58B,112C,123C 'attacker-control':122C 'code':68B,125C,152C 'compon':119C 'compromis':114C 'control':124C 'cve':13A,16A 'download':2A,20A,37B,100C 'execut':121C,153C 'fail':41B 'fetch':51B 'fiddler':1A,19A,29B,36B,99C 'influenc':116C 'instal':6A,91B,144C 'integr':45B,93C 'linux':30B,53B,105C 'local':79B,161C 'maco':12A,31B,54B,77B,106C,133C,168C 'may':150C,163C 'miss':92C 'packag':8A,49B,63B,85B,138C,169C 'path':142C 'predict':141C 'privileg':90B,148C,156C 'process':80B,162C 'progress':32B,97C 'releas':48B,118C 'replac':165C 'root':10A,89B,155C 'root-privileg':88B 'run':65B,72B,129C 'setup':3A,21A,39B,102C 'skill':5A,22A,25B,40B,74B,103C,131C,135C,172C 'softwar':98C 'stage':84B,136C,167C 'swap':82B 'tamper':60B 'telerik':33B 'tool':28B 'unverifi':7A 'user':71B,128C,158C 'verif':94C 'verifi':43B 'wait':173C 'window':34B,56B,108C","nicknames":[],"mitigations":[],"who_affected":"Teams that downloaded the Progress Telerik Fiddler Download & Setup Skill (fiddler-download-setup) before October 5, 2026 and run it in a coding agent on Linux, macOS or Windows. The skill fetches the Fiddler Everywhere installer without checking it against the manifest SHA-512 or a signature, so an attacker who compromises or influences a release component could run code when the skill is used. On macOS the package sits at a predictable /tmp path and installs as admin, so a malicious package could get root after you approve the prompt, and a local process could swap it while the skill waits. Teams that never used this skill, or use a current copy, can skip it.","tier":"B","verified":{"fix":{"at":"2026-11-06T17:46:23Z","by":"analyst","doc":"https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657","run_id":1915},"products":{"at":"2026-11-06T17:46:23Z","by":"analyst","doc":"https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657","run_id":1915},"how_to_check":{"at":"2026-11-06T17:46:23Z","by":"analyst","doc":"https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657","run_id":1915},"who_affected":{"at":"2026-11-06T17:46:23Z","by":"analyst","doc":"https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657","run_id":1915}},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"pkeys":["downloadsetupskill","fiddlerdownloadsetupskill"],"ptokens":["download","fiddler","setup","skill"],"labels":["aiskills","aitooling","fiddler","high","linux","macos","progress","telerik","windows"],"campaign_type":null,"search_a":"'-104657':15A,18A '-2026':14A,17A 'agent':4A 'cve':13A,16A 'download':2A,20A 'fiddler':1A,19A 'instal':6A 'maco':12A 'packag':8A 'root':10A 'setup':3A,21A 'skill':5A,22A 'unverifi':7A","search_b":"'ai':24B,27B 'ai-skil':23B 'ai-tool':26B 'attack':58B 'code':68B 'download':37B 'fail':41B 'fetch':51B 'fiddler':29B,36B 'instal':91B 'integr':45B 'linux':30B,53B 'local':79B 'maco':31B,54B,77B 'packag':49B,63B,85B 'privileg':90B 'process':80B 'progress':32B 'releas':48B 'root':89B 'root-privileg':88B 'run':65B,72B 'setup':39B 'skill':25B,40B,74B 'stage':84B 'swap':82B 'tamper':60B 'telerik':33B 'tool':28B 'user':71B 'verifi':43B 'window':34B,56B","search_c":"'administr':147C 'allow':110C,151C 'also':164C 'approv':159C,175C 'attack':112C,123C 'attacker-control':122C 'code':125C,152C 'compon':119C 'compromis':114C 'control':124C 'download':100C 'execut':121C,153C 'fiddler':99C 'influenc':116C 'instal':144C 'integr':93C 'linux':105C 'local':161C 'maco':106C,133C,168C 'may':150C,163C 'miss':92C 'packag':138C,169C 'path':142C 'predict':141C 'privileg':148C,156C 'process':162C 'progress':97C 'releas':118C 'replac':165C 'root':155C 'run':129C 'setup':102C 'skill':103C,131C,135C,172C 'softwar':98C 'stage':136C,167C 'user':128C,158C 'verif':94C 'wait':173C 'window':108C","first_public_at":"2026-11-06T17:17:11+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","cvss_by":"security@progress.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-104657","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-104657","severity":null,"published_at":"2026-11-06T17:17:11+00:00","modified_at":"2026-11-06T17:17:11+00:00","first_seen_at":"2026-11-06T17:43:11+00:00","fetched_at":"2026-11-06T17:43:11+00:00","note":null},{"source":"analyst","external_id":"CVE-2026-104657:1915","url":"https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657","severity":null,"published_at":"2026-11-06T17:46:23+00:00","modified_at":"2026-11-06T17:46:23+00:00","first_seen_at":"2026-11-06T17:46:23+00:00","fetched_at":"2026-11-06T17:46:23+00:00","note":"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.","cites":["https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657"]}],"documents":[{"id":88411,"url":"https://www.telerik.com/fiddler/fiddler-everywhere/documentation/knowledge-base/kb-security-missing-download-integrity-verification-cve-2026-104657","title":"Telerik KB: Download of Code Without Integrity Check (CVE-2026-104657)","kind":"advisory","source":"analyst","publisher":null,"text":null,"published_at":null,"relation":"advisory","confidence":null,"note":null}],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}