This may not be popular among your users, but I believe the only way you can know for sure is to force a password change for every SQL login with
CHECK_POLICY = ON. This will generate a set of
ALTER LOGIN commands with blank passwords, you can update the query giving them all a common password or manually update each one with individual passwords - just make sure they meet your policy. Of course you need to be sure that the password policy is as complex as you expect, and that it is enabled (Control Panel > Administrative Tools > Local Security Policy > Account Policies > Password Policy > Password must meet complexity requirements).
SELECT N'ALTER LOGIN ' + QUOTENAME(name)
+ N' WITH PASSWORD = N'''' MUST_CHANGE, CHECK_POLICY = ON;'
--WHERE is_policy_checked = 0;
Steve Jones wrote about this a while back. Note that - due to what I uncovered below - you can't rely on
is_policy_checked = 1 to mean that the password actually meets your current policy, since the login could have been created with a hashed password (in which case the plain text password can't be checked) or while the local complexity policy was disabled (which still leads to
is_policy_checked = 1).
Another approach I thought would work would be to try to create a copy of every login with their current
password_hash and with
CHECK_POLICY = ON, and make a note of every one that fails. However, this can not work - even with
CHECK_POLICY = ON, it doesn't perform any validation of an already-hashed password. I'll include the code for posterity - but, by design, the policy simply can't be checked.
SELECT N'BEGIN TRY
CREATE LOGIN ' + QUOTENAME(N'copy_of_' + name)
+ N' WITH PASSWORD = '
+ CONVERT(NVARCHAR(255), password_hash, 1)
+ ' HASHED, CHECK_POLICY = ON;
DROP LOGIN ' + QUOTENAME(N'copy_of_' + name) + ';
IF ERROR_NUMBER() = 15118
PRINT N''' + REPLACE(name, '''', '''''')
+ N' was not complex enough.'';
Personally, I think this is a bug. If the syntax allows me to create a login using a hashed password, and I can stipulate that that password must meet my complexity policy, it should generate an error or warning that the policy was not, in fact, checked.
UPDATE: I filed a bug against this behavior.