Fixing a Broken Migration Assistant Clone on macOS Tahoe

MacOS

Date: 2026-02-10
Host: new Mac (macOS Tahoe)
Context: Migration Assistant clone from older Mac failed

Unrecoverable error.

SecurityAgent was unable to create requested mechanism TeamViewerAuthPlugin:start.

Summary

First day using macOS Tahoe, immediately greeted with a broken Migration Assistant clone from an older Mac. The system failed to reach the login window due to a corrupted SecurityAgent authorization plugin left behind by TeamViewer. This caused login to fail and wedged Setup Assistant in a deadlock during post-migration initialization.

Root Cause

TeamViewer installs a SecurityAgent authentication hook:

/Library/Security/SecurityAgentPlugins/TeamViewerAuthPlugin.bundle

During migration, this plugin was partially migrated or left in an invalid state. macOS attempted to load:

TeamViewerAuthPlugin:start

Because the plugin was broken, SecurityAgent aborted authentication, preventing login and causing Setup Assistant / Migration Assistant to deadlock during post-boot user context initialization.

Fix

Booted into macOS Recovery, unlocked and mounted the system volume from Terminal, and removed the broken authorization plugin:

diskutil apfs unlockVolume diskXsY

rm -rf "/Volumes/Macintosh HD/Library/Security/SecurityAgentPlugins/TeamViewerAuthPlugin.bundle"

After plugin removal, macOS booted into:

โ€œTransferring your information, starting upโ€ฆโ€

At this point, Setup Assistant / Migration Assistant beachballed and deadlocked. Forced quit of the stuck setup flow followed by a reboot allowed the system to resume normal boot.

Once the broken login mechanism chain was removed and the hung setup process terminated, the login window appeared and the system completed startup normally.

Outcome

  • Login window restored
  • No data loss
  • Migration Assistant loop resolved
  • SecurityAgent no longer crashes
  • Normal boot path restored

Notes

For future migrations:

  • Uninstall TeamViewer before running Migration Assistant
  • Reinstall TeamViewer cleanly after migration
  • Avoid migrating software that hooks into macOS authentication mechanisms

Files / Paths Involved

/Library/Security/SecurityAgentPlugins/TeamViewerAuthPlugin.bundle