Released: 2025 H1 Cumulative Update for Exchange Server

The_Exchange_Team, Nino_Bilic , at the very least, can you add a known issue to the CU15 release information that indicates that the web.config file will be overwritten? 

It seems web.config is overwritten so that this line can be added:

<linkedConfiguration href="file://C:\Program Files\Microsoft\Exchange Server\V15\bin\SharedBindingRedirects.config" />

(or at least that's the only addition on my installation from 2019 CU14 Nov24SUv2 to 2019 CU 15).

To double check this, I reviewed a backup prior to CU15 install.

The SharedBindingRedirects.config file DOES NOT exist before I installed CU15 on Feb 12: 

web.config was created/last modified in May/June of 2024:

Then, I reviewed a backup after the CU15 install.

The SharedBindingRedirects.config file DOES exist after I installed CU15 on Feb 12: 

web.config was created when I started the install at 10:01pm, and modified at 10:18pm when I subsequently re-added the alternateHostName attribute:

Unfortunately, overwriting the web.config file removes all custom headers and URL Rewrite rules (and potentially other things) for Exchange.

(Maybe it's just me, though I'd be surprised because I'm literally diffing web.config and comparing backups before and after the CU15 upgrade.  I guess what's more surprising is that more people haven't noticed this or aren't having issues caused by this, which, of course, has me second guessing myself.)

Either way, I believe I've fixed this on my side, but if true, others should be made aware as well.

Thanks, as always!