macOS includes a robust security feature known as Gatekeeper. Whenever you download a new application from the internet and attempt to open it for the first time, a background system service called CoreServicesUIAgent intercepts the launch. It scans the app for malware and verifies the developer’s digital signature, displaying a small progress bar titled “Verifying [App Name]…”
Occasionally, this verification process completely freezes. The progress bar gets stuck at 90%, the application refuses to open, and you cannot even click the ‘X’ to close the verification window. This happens when the CoreServicesUIAgent process crashes or hangs while trying to communicate with Apple’s security servers. To fix this, you must forcefully terminate the frozen background agent.
How to Fix a Stuck “Verifying App” Window on a Mac
Because the CoreServicesUIAgent is a background system process, it will not appear in the standard “Force Quit Applications” menu (Option + Command + Escape). You must use the Activity Monitor to kill it.
- Open the Finder, go to Applications, open the Utilities folder, and double-click Activity Monitor (or press Command + Space and search for Activity Monitor).
- In the Activity Monitor window, ensure the CPU tab is selected at the top.
- Look at the search bar in the top-right corner of the window. Type the following exact phrase:
CoreServicesUIAgent - The main list will filter down to show this single process. It will likely have “(Not Responding)” written next to it in red text.
- Click on the CoreServicesUIAgent process to highlight it.
- Click the X icon (Stop) located at the very top of the Activity Monitor toolbar.
- A confirmation dialog will appear. Click the Force Quit button.
The stuck “Verifying…” window will instantly disappear from your screen. You can now try double-clicking the original application again. The macOS operating system will automatically launch a fresh, unfrozen instance of the verification agent, which should successfully scan the app and allow it to open normally.