Apple has just released a surprise update to macOS 10.15 Catalina, bringing it to version 10.15.7.

At around 2.6 GB, it’s relatively small, and fixes a number of important issues, including problems connecting automatically to Wi-Fi networks, failure to sync files through iCloud Drive, and problems with Radeon Pro 5700 XT graphics support on the latest iMac Retina 5K, 27-inch, 2020.

This is accompanied by Security Updates for High Sierra and Mojave. The initial release of Mojave Security Update 2020-005 has caused widespread problems: for the moment, it seems wise not to install it. Further details are given below.

Security fixes are detailed for all three here. There are only four in total, of which two apply to Catalina. The most serious of them, which affects all three versions of macOS, is a sandbox vulnerability which gives access to restricted files (CVE-2020-9968).

There are no new firmware updates provided.

Oddly, this update installs an old version of Apple’s Malware Removal Tool, MRT, 1.62. Once the installation is complete, you should be able to download and install an update to bring back up to 1.66, which is the same version prior to this update.

Standalone updaters are now available as follows:

• for 10.15.7, the ‘delta’ update, and Combo update;
• for 10.14, Mojave Security Update 2020-005
• for 10.13, High Sierra Security Update 2020-005

I have now analysed the changes brought in 10.15.7, which you can read about in detail here.

Postscript: Many users are reporting problems following installation of the initial release of Mojave Security Update 2020-005. These range from minor, such as warnings when running softwareupdate, to major problems with memory usage and impaired performance. These are detailed here by Mr Macintosh, and extensively across other Mac sites.

Minor problems after any of these updates can be resolved by restarting in Safe mode, then after a couple of minutes restarting normally. More severe issues can be resolved by rolling back to a pre-update snapshot (if you’re running Time Machine), by re-installing Mojave, or by upgrading to Catalina (which is being suggested by Apple). However 10.15.7 isn’t without its own glitches. I’ll be taking a look at these updates in more detail on Monday 28. If you haven’t updated yet, you might like to hold off for now, as Apple may well replaced one or more of them.

(Updated 0740 UTC 27 September 2020.)