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Researchers Flag Account Takeover Flaw in Microsoft Azure AD OAuth Apps

Businesses using ‘Log in with Microsoft’ could be exposed to privilege escalation and full account takeover exploits.

NET vulnerability CVE-2023-38180 exploited

Researchers at security startup Descope have discovered a major misconfiguration in Microsoft Azure AD OAuth applications and warned that any business using ‘Log in with Microsoft’ could be exposed to full account takeover exploits.

The security defect, nicknamed nOAuth, is described as an authentication implementation flaw that can affect Microsoft Azure AD multi-tenant OAuth applications. 

According to an advisory documenting the issue, Descope noted that a malicious actor can modify email attributes in Microsoft Azure AD accounts and exploit the one-click “Log in with Microsoft” feature with the email address of any victim they want to impersonate. 

“In usual OAuth and OpenID Connect implementations, the user’s email address is used as the unique identifier by applications. However, in Microsoft Azure AD, the “email” claim returned is mutable and unverified so it cannot be trusted,” Descope explained.

The company said the combined effect allows an attacker that created their Azure AD tenant to use “Log in with Microsoft” with a vulnerable app and a specially crafted “victim” user, resulting in a complete account takeover. Descope released a demo video showing the simplicity of potential exploitation.

Descope, a startup in the customer identity space, reported the issue to Microsoft earlier this year and worked with Redmond on new mitigations to protect businesses from privilege escalation attacks.

Microsoft described the issue as “an insecure anti-pattern used in Azure AD (AAD) applications” where use of the email claim from access tokens for authorization can lead to an escalation of privilege. 

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“An attacker can falsify the email claim in tokens issued to applications. Additionally, the threat of data leakage exists if applications use such claims for email lookup,” Microsoft acknowledged.  

“Microsoft recommends never using the email claim for authorization purposes. If your application uses the email claim for authorization or primary user identification purposes, it is subject to account and privilege escalation attacks,” the software giant said.

Microsoft is also urging developers to review the authorization business logic of their applications and follow documented guidance to protect applications from unauthorized access.  

Related: Descope Targets Customer Identity Market with Massive $53M Seed Round

Related: Microsoft Warns of High-Severity Vulnerability in Azure AD

Related: Microsoft Fixes Privilege Escalation Flaw in Azure AD Connect

Related: Microsoft Patches Azure Cosmos DB Code Execution Flaw

Written By

Ryan Naraine is Editor-at-Large at SecurityWeek and host of the popular Security Conversations podcast series. He is a security community engagement expert who has built programs at major global brands, including Intel Corp., Bishop Fox and GReAT. Ryan is a founding-director of the Security Tinkerers non-profit, an advisor to early-stage entrepreneurs, and a regular speaker at security conferences around the world.

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