SOLVED: first-time login problems when enforcing MFA with AWS

AWS has a tutorial about enforcing MFA for all users. The general thrust of the article is to create a policy that allows users without MFA to do nothing other than log in and set up MFA. Having enabled and logged in using MFA, other permissions become available to the user (according to whatever other permissions are assigned).

This works well apart from one snag: having created a user, and set the flag forcing the user to change password on first login, the user cannot log in. Instead the user is greeted with the following error:

Either user is not authorized to perform iam:ChangePassword or entered password does not comply with account password policy set by administrator

The problem lies in a policy statement called “DenyAllExceptListedIfNoMFA”. As its name suggests, for a user without MFA, this blocks all bar the specified actions. In AWS’s recommended policy, the section effectively allows the following actions:

"iam:CreateVirtualMFADevice",
"iam:EnableMFADevice",
"iam:GetUser",
"iam:ListMFADevices",
"iam:ListVirtualMFADevices",
"iam:ResyncMFADevice",
"sts:GetSessionToken"

You’ll notice that those actions don’t include anything about changing a password! So without MFA already enabled on your account, there’s no way to change your password when first logging on (if “force password change” is enabled). The trick is to add two more permissions:

"iam:ChangePassword",
"iam:CreateLoginProfile",

For a user that has not yet logged into the AWS console, this will allow creation of the user’s login profile and setting a new password.