The surprise update to Big Sur, bringing it to version 11.5.2, is the first that I can recall that has absolutely no release notes at all: none for users, who are merely told that it “includes bug fixes”, none for system administrators, and no security release notes. Apple has left us completely in the dark, except …

This is more than a minimal update, such as 11.5.1 which fixed a single vulnerability. Intel Macs get a little over 2.5 GB, and M1 Macs 3.45 GB, suggesting it has an effective payload of about 300 MB of “bug fixes”. For those running a local Content Caching Server, M1 Macs still need to download the first 910 MB of this update direct from Apple’s servers, so there has been no improvement in this update in terms of efficiency.

There don’t appear to be any firmware updates, except possibly for some Intel Macs which lack a T2 chip. There’s no change in the T2 firmware, nor in the iBoot version number of M1 Macs. There’s no change in the Darwin kernel, which remains at version 20.6.0: Wed Jun 23 00:26:31 PDT 2021; root:xnu-7195.141.2~5, and the macOS version changes from 11.5.1 (Build 20G80) to 11.5.2 (Build 20G95).

There are no changes in version or build number in any of the main bundled apps (those in /Applications and /Applications/Utilities), and Safari remains at version 14.1.2, although its build number increases from 16611.3.10.1.3 to 16611.3.10.1.6.

Notable changes in version or build number in components in /System/Library include:

• Problem Reporter.app in CoreServices, and its Private Framework CrashReporterSupport, have a tiny increment in build number, from 15053 to 15053.1
• AppKit framework has a small increment in build number, from 2022.60.126 to 2022.60.128
• FileProvider framework has a small increment in version number, from 349.4.2 to 349.4.3 (build numbers are the same as its version numbers)
• JavaScriptCore framework has a small increment in build number, to 16611.3.10.1.6
• QuartzCore framework has a single digit increment in build number, to 927.24
• SafariServices and WebKit frameworks have an incremented build number to match that of Safari
• Among other private frameworks to have minor increments in build number are FileProviderDaemon, and other Safari frameworks.

It appears that the bugs which this fixes in Safari and those frameworks were deemed significant enough to merit a ‘patch’ update before Big Sur goes into security-only maintenance on the release of Monterey. But to release a 3.45 GB update without explaining what it’s supposed to fix is about the most unhelpful thing that Apple could do just over two weeks after the last 3.1 GB update.