An elevation of privilege vulnerability exists in Azure Active Directory Authentication Library On-Behalf-Of flow, in the way the library caches tokens, aka 'Azure Active Directory Authentication Library Elevation of Privilege Vulnerability'.

An elevation of privilege vulnerability exists in Azure Active Directory Authentication Library On-Behalf-Of flow, in the way the library caches tokens. This vulnerability allows an authenticated attacker to perform actions in context of another user.
The authenticated attacker can exploit this vulneraiblity by accessing a service configured for On-Behalf-Of flow that assigns incorrect tokens.
This security update addresses the vulnerability by removing fallback cache look-up for On-Behalf-Of scenarios.