Recently when adding a catalog to the third party software update catalogs in SCCM Current Branch 1806 and trying to synchronize, I encountered the error “Unable to create the subscription. The console failed to download <product> from <URL> because of the error code 13875. For more information, see SmsAdminUI logfile.”
The error code 13875 means “Invalid certificate signature“. For more troubleshooting I downloaded the cab file by opening up IE and pasting in the link. Once the cab file was downloaded, I right clicked on the file then properties, clicked Digital Signatures tab:
Then here my issue was that the certificate in the signature could not be verified. I clicked on View Certificate to view more details.
My issue was that on the client server, it was missing some Trusted Root certificates. After these were installed the third party updates could then be synchronized to SCCM Current Branch 1806 without issues.