A new Microsoft Teams app or bot was observed

microsoft-365

Classification:

attack

Tactic:

TA0003-persistence

Technique:

T1137-office-application-startup

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Goal

Detect when a new Microsoft 365 teams app or bot is installed as a means of establishing persistence.

Strategy

Monitor Microsoft 365 audit logs to look for events with an @evt.name value of AppInstalled, where the AddOnType has a value of 1 OR 4 and a new @AddOnName is observed.

According to Microsoft, the following values indicate the types of add-ons that exist:

  • 1 - Indicates a bot.
  • 2 - Indicates a connector.
  • 3 - Indicates a tab.

However, some add-ons use the value 4 for existing teams apps that could be potentially unapproved bots or applications that could be malicious.

Triage and response

  1. Determine if the user {{@usr.email}} intended to install {{@AddOnName}}.
  2. If {{@usr.email}} is not responsible for installing {{@AddOnName}}, investigate {{@usr.email}} for anomalous activity. If necessary, initiate your company’s incident response (IR) process.

Changelog

Updated rule name and query to include bots.