CVE-2019-1258: Microsoft Active Directory Authentication Library

High severity, CVSS 8.8. EPSS: 3.8% chance of exploitation in the next 30 days.

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.

Affected products

• Microsoft Active Directory Authentication Library: from 5.0.5, before 5.2.0 (fixed in 5.2.0); version 5.0.0 only; version 5.0.1 only; version 5.0.2 only; version 5.0.3 only
• Microsoft Nuget: version 5.2.0 only

Published 2019-08-14. Last modified 2026-06-17.