Apple has just released macOS Catalina 10.15.7 Supplemental Update, which weighs in at around 1.2 GB and includes important security fixes for two kernel vulnerabilities and a FontParser bug. All three of these are currently being exploited in the wild, which explains the urgency in patching them.
It’s currently available via Software Update. As soon as I have a link to the standalone installer package I will update this article, but as of 2105 UTC I can’t find any. Details of the three security fixes it includes are given here.
There are no changes in version or build number of any of the bundled apps, nor are there in any of the significant contents of /System/Library. There don’t appear to be any firmware updates, at least not for Macs with a T2 chip. This suggests that this quite hefty update is mainly a new kernel, which isn’t bad for more than a GB!
One significant feature of this update is that it reverts MRT to an old version, around 1.62. Immediately after updating you’ll want to run SilentKnight or LockRattler to restore MRT to its current version 1.69.3. For the record, on this occasion I used the latest version of SilentKnight to download the MRT update then installed it manually by double-clicking the Installer package. This worked fine, and even ran the new MRT for its initial scans just as if it had been installed by
HT to Mr Macintosh for the warning.
Updated 2110 UTC 5 November 2020.