file is damaged and can’t be opened. You should move it to the Trash.

On my 2013 27" iMac, turning off SIP was the solution to my systems problems after macOS 10.15.2 was installed, at which point, everything in the Downloads folder gave the error message “file is damaged and can't be opened”.   This behavior was also true for any attachment downloaded from Apple Mail, any downloaded installer file (.dmg or package).  After SIP was disabled via the Terminal command csrutil disable in the Recovery mode, these symptoms disappeared completely. When I enabled SIP once again by rebooting my system, this anomalous behavior returned, with the "file is damaged" message being displayed (for files that were not, in fact, damaged at all).

Problem resolved under guidance from Apple Support. Permissions to whole of Home folder reset via "Home Folder, Get Info, Sharing & Permission, Apply to enclosed items...."

Determined to be an OS level problem.

Thanks to all for help and suggestions in diagnosis.

I encountered this issue this morning at a client's office when working on their two laptops. A MacBook Air and a MacBook Pro. Both were running macOS Catalina 10.15.3.

The MacBook Pro would not open any downloaded .DMG files saying they were damaged (as per this post). The MacBook Air was fine accessing the same files.

I discovered that all the downloaded files had been given a com.apple.quarantine flag in the xattr. After removing the quarantine flag all files were able to be opened normally. The command used was xattr -d com.apple.quarantine * from within the ~/Downloads directory

This however does not address why they were flagged in the first place, nor preventing new files from being flagged upon download.

I'd be very interested if someone else has some insight into this.

Well the "sum" results for both are exactly the same, yet Catalina says the file is corrupt and Mojave is happy with it, which doesn't seem possible. So perhaps the attributes are what is causing the problem?

Wonder what would happen if you removed all the special attributes from the install_backblaze.dmg file -- perhaps you could try the following and then try and mount the dmg file:

xattr -d com.apple.lastuseddate#PS install_backblaze.dmg 
xattr -d com.apple.macl install_backblaze.dmg 
xattr -d com.apple.metadata:kMDItemDownloadedDate install.backblaze.dmg
xattr -d com.apple.metadata:kMDItemWhereFroms install_backblaze.dmg

Does that make any difference on the ability to mount the install_backblaze.dmg file?

Is it possible to give an explicit example of a file (dmg, app, etc) that fails for you, that I could try and download on my Catalina 10.15.2 system to see how my results compare to yours? If so, please give a URL and will give it a try and let you know how things turn out.

I just tried to download a copy of MacTracker.app from https://mactracker.ca and it worked fine, so the problem is not present for all Catalina 10.15.2 systems (the only file attribute on the Mactracker.app package was the com.apple.quarantine with a value of 57 (so none of others that you had on your install_backblaze.dmg file).

Good luck...

I may have spoke too soon. It mostly seems to work. However, any file I now download from the internet has that problem. It says it is damaged. If xattr -cr on the file I can get it to work and open. So it seems the files are fine, but some kind of extended attribute is being added at download which breaks the file. Could SIP be corrupted? It seems like it is reading files wrong.

I recently updated my 2013 27" iMac to macOS 10.15.2 Catalina, and found that I needed to update applications such as BackBlaze and TechTool Pro on my system. Downloaded the .dmg files and when I tried to open them, got the now infamous error message: "filename.dmg" is damaged and can't be opened. You should move it to the Trash."

To test if this was true, I returned to my MacBook Pro running macOS 10.14 Mojave, downloaded the BackBlaze installer dmg file and successfully opened it on that system. Once the installer disk image was mounted on my desktop, I copied the installer App from that disk image and pasted it into a new folder in my iCloud Drive (in use on both the MBPro and on the iMac running Catalina). Back on the iMac, running Catalina, I used Command + Open to open the installer Application for Back Blaze, then answered the system security questions that yes, in fact, I did want to open that application. The installer application ran successfully in Catalina. Repeated the process for the TechTool Pro installer -- an Installer Package file -- copying it to the iCloud Drive folder. Repeated the Command + Open technique for the TechTool Pro Installer, but this time it did not work -- got the same "file is damaged" message. Have not found a work-around for this... yet. Hope this helps.

Well, I downloaded the URL onto my Catalina 10.15.2 and it mounts fine. The dmg file is the same size that you show but does not have the same attributes. These are the attributes I see on my Catalina 10.15.2 system (note that the first two attributes are added as soon as the dmg file is mounted):

user@My-Mac Downloads % ls -lae@ install_backblaze.dmg 
-rw-r--r--@ 1 user  staff  17658479 Jan  4 17:28 install_backblaze.dmg
	com.apple.diskimages.fsck	      20 
	com.apple.diskimages.recentcksum	      78 
    com.apple.lastuseddate#PS	      16 
	com.apple.metadata:kMDItemDownloadedDate	      53 
	com.apple.metadata:kMDItemWhereFroms	     101 
	com.apple.quarantine	      57 
user@My-Mac Downloads % sum install_backblaze.dmg 
3423 17245 install_backblaze.dmg
user@My-Mac Downloads % df -kt /Volumes/Backblaze\ Installer 
Filesystem  1024-blocks Used Available Capacity iused      ifree %iused  Mounted on
/dev/disk6s1  29300    25976      3324    89%     178 4294967101    0%   /Volumes/Backblaze Installer

The only thing rather out-of-the-ordinary on my system is a special SIP setup. It's not disabled but it has the following status:

user@My-Mac Downloads % csrutil status
System Integrity Protection status: unknown (Custom Configuration).

Configuration:
	Apple Internal: disabled
	Kext Signing: disabled
	Filesystem Protections: disabled
	Debugging Restrictions: disabled
	DTrace Restrictions: disabled
	NVRAM Protections: disabled
	BaseSystem Verification: disabled

This is an unsupported configuration, likely to break in the future and leave your machine in an unknown state.

You might try disabling SIP to see if that is the cause of this problem, but that is up to you, as that has other security implications. If you want to try, boot up in Recovery mode and issue the command in a Terminal window:

csrutil disable

and then reboot in normal mode. Note that this is a one time change, in the sense that another reboot will put SIP back in the default, enabled, mode.

Good luck...

Using the Terminal command "sum" do the two downloads show the same results? Are the file permissions and attributes the same? Try something like this in Terminal on both MacBook Pro and iMac systems:

uname -a
ifconfig -a
cd /folder-containing-dmg
sum filename.dmg
ls -lae@ filename.dmg

Post the results for both (change any personal info that you don't want public like username, IP address and ethernet hardware id) and maybe we can see what might be causing the problems. If you need more info, just ask.

Good luck...

I have experienced similar problems with 10.14.6. I was about to go to 15.2 when I read this post, so I have now hesitated to upgrade.

A couple of weeks ago I downloaded ScummVM from Ubisoft so that I may re-install my copy of Riven (5 CDs) and play it again. When I downloaded the installer I got the same message as you about the file being corrupted and moving it to the trash.

I found an answer in the Mojave forum here. The answer had me go into System Preferences/Security & Privacy/General then look for where it says -

“Allow apps downloaded from:

• Apple Store
• App Store and identified developers.

I then followed a very short instruction to use Terminal to disable a setting in GateKeeper. Just a short line that I could copy/paste.

Following this I now had a third option -

• Allow from everyone.

After unlocking the pane and choosing this previously hidden option the downloaded files worked fine.

The instruction then showed me how to use Terminal to re-enable GateKeeper by using the same instruction say ‘enable' instead of ‘disable'. Although in practice it appears to have re-enabled itself at some point in time.

You will find the post in the Mojave forum. I think it may have been about three years old. I will look to see if I can find it again. If I find it I will post back with the link.

Bring up the Info pane for that file and see if there's an Admin user listed in the Ownership & Permisions section. If not add it and make all of the users listed Read & Write. Then try to open the file.

This problem has been driving me crazy. The fix so far that worked for me was to turn off SIP protection restart check my files were working and then re-enable it. So far so good.

On a file that gives you that error message set the permissions to Read & Write for the owner (you), the group that it's associated with and for everyone. Then see if you can open it.

It is a general problem not related to file type. Turning off SIP resolves the problem. But re-enabling it brings it back.

Hello again. OK -- I ran the terminal commands as you suggested on the install_backblaze.dmg file on my desktop in Catalina, then tried to mount it, but still get the error message as show below

Note that after running the terminal commands as you suggested, and repeating the ls -lae@ install_backblaze.dmg in Terminal, I get these results:

-rw-r--r--@ 1 username  staff  17658479 Jan  3 13:54 install_backblaze.dmg

com.apple.macl       72 

com.apple.quarantine       57 

The source for this file is at this URL -- see if you can download it on your system, and if you can get it to open on your machine running macOS 10.15.2: Download for Mac