macOS "App is Damaged" Warning: Why It Happens and How to Fix It

macOS uses a security mechanism called Gatekeeper to protect users from malicious software. Gatekeeper expects applications downloaded from the internet to be signed with an Apple Developer certificate and notarized by Apple. When an app fails those checks, macOS may refuse to launch it — and the message it shows is often the alarming "is damaged and can't be opened."

A note about OpenGnothia: current builds are signed with an Apple Developer certificate and notarized by Apple, so they open normally, with no warning and no workaround needed. Earlier releases were distributed unsigned, so a very old download you kept around may still trigger this. The rest of this guide explains the warning in general — it applies to any app, from any developer, that Gatekeeper cannot verify.

The warning does not mean the file is actually damaged or that it contains malware. It is simply macOS's response to an app whose signature it cannot check. A genuinely corrupted download is possible, but it is far less common than a signing issue.

Gatekeeper is one of macOS's built-in security features. Since macOS Catalina (10.15), security policies have been further tightened. Gatekeeper operates at three levels: apps downloaded from the App Store (most trusted), signed apps from identified developers, and apps from unknown sources.

When you download a file from the internet, macOS adds a special attribute called com.apple.quarantine (an extended attribute) to the file. When the app is first opened, Gatekeeper checks this attribute and evaluates the application's trustworthiness.

For unsigned apps, Gatekeeper may show two different warnings: "[App] can't be opened because Apple cannot check it for malicious software" or the more severe "[App] is damaged and can't be opened. You should move it to the Trash." The second warning is particularly common on macOS Ventura and later.

To fix this, you remove the quarantine attribute that macOS attached to the file when you downloaded it. This is safe and only clears the download flag — it does not modify the app itself.

Step 1: Open the Terminal application. Press Command + Space to open Spotlight, type "Terminal", and press Enter.

Step 2: Type the following command, replacing AppName with the actual name of the app, then press Enter:

xattr -cr /Applications/AppName.app

If the app is still in your Downloads folder rather than Applications, point the command there instead:

xattr -cr ~/Downloads/AppName.app

A useful shortcut: type "xattr -cr " with a trailing space, then drag the app from Finder into the Terminal window. macOS fills in the exact path for you, which avoids typos.

Step 3: After running the command, open the app normally. macOS will no longer treat it as quarantined.

The xattr command is used to manage extended attributes on files in macOS. Here's what the flags in our command mean:

The -c flag: Clears all extended attributes from the file (clear). This includes the com.apple.quarantine attribute.

The -r flag: Applies the operation to subfolders as well (recursive). A .app file is actually a folder structure, so we need to clear all sub-files too.

This command only modifies file attributes — it does not affect the application itself or your system settings. It is completely safe to use.

If you prefer not to use Terminal, you can also try to resolve the issue through macOS System Settings, although this method does not always work.

Step 1: Try to open the app, receive the warning, and dismiss it.

Step 2: Go to System Settings > Privacy & Security.

Step 3: Near the bottom of the page, you'll see a message like "[App] was blocked from use because it is not from an identified developer." Click the "Open Anyway" button next to it.

Step 4: Another confirmation dialog will appear — click "Open."

Note: If you're getting the harsher "is damaged" warning rather than the "cannot be checked" one, this method usually will not work, because macOS never offers the override button at all. In that case, use the Terminal method above.

I ran the xattr command but the app still won't open. What should I do? First make sure you used the correct path — run ls /Applications/ in Terminal to confirm the app is actually there. Also make sure you dragged the app out of the mounted DMG into Applications; running an app from inside a DMG causes problems of its own. If it still fails, the download may genuinely be corrupt, so download it again.

Is this safe? The command itself is safe: xattr -cr only removes metadata that macOS attached to the file, and it does not modify the app's code or change your system security settings. The judgement call is what you point it at. Clearing the quarantine flag is exactly what stops Gatekeeper from checking the app, so only run it on software from a source you actually trust.

Do I need to do this after every update? Only for unsigned apps. macOS attaches a fresh quarantine attribute to every new download, so an unsigned app needs the command again after each update. Properly signed and notarized apps — including current versions of OpenGnothia — never need it.

Does this issue occur on Windows or Linux? No, this specific warning comes from macOS's Gatekeeper. Windows has a comparable feature in SmartScreen, but it shows a different warning with its own "Run anyway" option. Linux has no equivalent gatekeeping by default.