Application Access Token

Adversaries may use application access tokens to bypass the typical authentication process and access restricted accounts, information, or services on remote systems. These tokens are typically stolen from users and used in lieu of login credentials.

Application access tokens are used to make authorized API requests on behalf of a user and are commonly used as a way to access resources in cloud-based applications and software-as-a-service (SaaS).[1] OAuth is one commonly implemented framework that issues tokens to users for access to systems. These frameworks are used collaboratively to verify the user and determine what actions the user is allowed to perform. Once identity is established, the token allows actions to be authorized, without passing the actual credentials of the user. Therefore, compromise of the token can grant the adversary access to resources of other sites through a malicious application.[2]

For example, with a cloud-based email service once an OAuth access token is granted to a malicious application, it can potentially gain long-term access to features of the user account if a "refresh" token enabling background access is awarded.[3] With an OAuth access token an adversary can use the user-granted REST API to perform functions such as email searching and contact enumeration.[4]

Compromised access tokens may be used as an initial step in compromising other services. For example, if a token grants access to a victim’s primary email, the adversary may be able to extend access to all other services which the target subscribes by triggering forgotten password routines. Direct API access through a token negates the effectiveness of a second authentication factor and may be immune to intuitive countermeasures like changing passwords. Access abuse over an API channel can be difficult to detect even from the service provider end, as the access can still align well with a legitimate workflow.

ID: T1527
Tactic: Defense Evasion, Lateral Movement
Platform: SaaS, Office 365
Permissions Required: User
Data Sources: OAuth audit logs, Office 365 account logs
Defense Bypassed: Multi-Factor Authentication, Logon Credentials
Contributors: Mark Wee; Jeff Sakowicz, Microsoft Identity Developer Platform Services (IDPM Services); Saisha Agrawal, Microsoft Threat Intelligent Center (MSTIC); Shailesh Tiwary (Indian Army)
Version: 1.0

Procedure Examples

Name Description
APT28

APT28 has used several malicious applications that abused OAuth access tokens to gain access to target email accounts, including Gmail and Yahoo Mail.[6]

Mitigations

Mitigation Description
Audit

Administrators can set up a variety of logs and leverage audit tools to monitor actions that can be conducted as a result of OAuth 2.0 access. For instance, audit reports enable admins to identify privilege escalation actions such as role creations or policy modifications, which could be actions performed after initial access.

Encrypt Sensitive Information

File encryption should be enforced across email communications containing sensitive information that may be obtained through access to email services.

Restrict Web-Based Content

Update corporate policies to restrict what types of third-party applications may be added to any online service or tool that is linked to the company's information, accounts or network (example: Google, Microsoft, Dropbox, Basecamp, GitHub). However, rather than providing high-level guidance on this, be extremely specific—include a list of pre-approved applications and deny all others not on the list. Administrators may also block end-user consent through administrative portals, such as the Azure Portal, disabling users from authorizing third-party apps through OAuth and forcing administrative consent.[5]

Detection

Monitor access token activity for abnormal use and permissions granted to unusual or suspicious applications. Administrators can set up a variety of logs and leverage audit tools to monitor actions that can be conducted as a result of OAuth 2.0 access. For instance, audit reports enable admins to identify privilege escalation actions such as role creations or policy modifications, which could be actions performed after initial access.

References