Dealing with a partially installed Windows 7 update

On one computer the June 2017 monthly rollup (KB4022719) somehow installed improperly or got corrupted. It couldn't be uninstalled, and future rollups couldn't be installed. Apparently, the process of installing a new rollup first needs to uninstall the previous one.

The Windows Update user interface simply gave the useless 80004005 error, but detailed information about the failure was available in c:\windows\logs\cbs\cbs.log:

2017-12-28 20:54:05, Error                 CBS    Failed. Attempted to uninstall a version of a non-driver component that is not installed, version: 0X700061db15cfe, component: amd64_microsoft-windows-w..lient-aux.resources_31bf3856ad364e35_7.6.7601.23806_en-us_e79af1b12d6db6c9, owner: Package_835_for_KB4022719~31bf3856ad364e35~amd64~~6.1.1.6.4022719-2919_neutral_LDR [HRESULT = 0x80004005 - E_FAIL]

Each update is a package which refers to many other packages, like Package_835_for_KB4022719~31bf3856ad364e35~amd64~~6.1.1.6.4022719, and each of those packages refers to components, like 2919_neutral_LDR. If you're curious, you can unpack an update and look inside it. First unpack the .msu to get the CAB and then unpack the CAB. You probably must use Microsoft's expand.exe to unpack the CAB because it may use intra package delta (IPD) compression which is not supported by 7-Zip.

Inside the CAB you will find various .mum files, which correspond to the main package and those sub-packages. The logical thing to do would be to reinstall these problematic components. However, I don't see a way to install from a .mum file.

So, I ended up uninstalling the messed up update by editing its already installed .mum file, found in c:\windows\servicing\packages, as  package_for_kb4022719_sp1~31bf3856ad364e35~amd64~~6.1.1.6.mum. (Note the absence of a number after "package" in the file name.) That directory is set up by default so only TrustedInstaller can write there. Not even SYSTEM can write there! So, I had to temporarily grant access to Administrators. The sections to remove are like this:

<update name="4022719-4117_neutral_PACKAGE">
<package integrate="hidden">
<assemblyIdentity name="Package_835_for_KB4022719" version="6.1.1.6" language="neutral" processorArchitecture="amd64" publicKeyToken="31bf3856ad364e35" />
</package>
</update>

After removing the sections referring to messed up sub-packages, it was possible to uninstall the rollup. However, reinstalling it didn't fix the problem. I guess the messed up partly installed sub-packages don't get reinstalled? Fortunately, I was able to install the December roll-up without problems. Hopefully future roll-ups will install, and the only consequences will be a few small unnecessary but harmless files and registry entries.