Apple has just released the update to bring Catalina to version 10.15.3, together with Security Updates for both Mojave and High Sierra. It reports two specific improvements in 10.15.3:

• optimises gamma handling for the Pro Display XDR,
• improves video editing performance in HEVC and H.264 4K video on the latest MacBook Pro 16-inch

but as the download amounts to around 3.42 GB and brings firmware updates for most models, I’m sure there’s a great deal more.

No further details are given in this article, but full security notes for all three updates are here.

Security fixes include updating PHP to version 7.3.11, a Gatekeeper bypass from an NFS mount, two remote Bluetooth attacks, vulnerbility to crafted JPEG images, five kernel bugs, validation of symlinks in packages, and a remote Wi-Fi attack. From a security viewpoint alone, these are essential updates.

Standalone updaters for 10.15.3 are already available. The ‘delta’ update for 10.15.3 is here, and the Combo updater for 10.15.3 is here [NOTE: Apple has now corrected this for the US version of this page, in the link given here. Other locales may take longer to propagate the correct page]. Security Update 2020-001 for Mojave is here, and for High Sierra is here.

I have now updated the firmware versions in SilentKnight’s database and the lists here, thanks to Pico’s help in providing the new version details.