Logins, SIDs, and Kerberos from First Principles, Part 5: Windows Groups and the Invisible Members
Every post in this series so far has dealt with principals you can see: a login row in sys.server_principals with a name and a SID. Windows groups break that comfortable assumption. Grant a group a…
Logins, SIDs, and Kerberos from First Principles, Part 3: Migrating Logins Without Losing Them
Server migrations have a predictable failure mode: the databases restore perfectly, the application connection strings are updated, and then nothing can log in. Or worse, everything can log in but half the database users are…
Logins, SIDs, and Kerberos from First Principles, Part 2: The Vanishing Service Account
Years ago at a previous employer, I wrote a fleet-sweep script that searched every SQL Server instance in the estate for a specific service account, by name and by a known-bad SID. I no longer…
Logins, SIDs, and Kerberos from First Principles, Part 1: What a SID Actually Is
Ask SQL Server who you are and it will answer with a name. Ask it to make a decision about you, though, and it uses something else entirely: a security identifier, or SID. Names are…
Is Your SQL Server Using RC4 for Kerberos? Here’s How to Find Out
You probably haven’t thought about Kerberos encryption types recently. That’s fair; the protocol mostly “just works” and has for decades. But CVE-2026-20833 changed the calculus. Microsoft disclosed a Kerberos information disclosure vulnerability in January 2026…