One of the things TfL have done in their containment phase is locked their IT staff's accounts, who aren't working on recovery -- and they're working to manually reauthenticate who their staff are, i.e. check their identities.
In entirely unrelated (👀) news, teenagers in LAPSUS$ and Scattered Spider often obtain access by calling up the helpdesk and saying they've lost their phone for MFA and/or forgot their password.