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Azure Entra MFA TOTP Brute Force Attempts

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Azure Entra MFA TOTP Brute Force Attempts

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Identifies brute force attempts against Azure Entra multi-factor authentication (MFA) Time-based One-Time Password (TOTP) verification codes. This rule detects high frequency failed TOTP code attempts for a single user in a short time-span. Adversaries with valid credentials, when attempting to login to Azure portal or other Azure services, may be prompted to provide a TOTP code as part of the MFA process. If successful, adversaries can bypass MFA and gain unauthorized access to Azure resources.

Rule type: esql

Rule indices: None

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Cloud
  • Domain: SaaS
  • Data Source: Azure
  • Data Source: Entra ID
  • Data Source: Entra ID Sign-in
  • Use Case: Identity and Access Audit
  • Use Case: Threat Detection
  • Tactic: Credential Access

Version: 1

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

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Triage and Analysis

Investigating Azure Entra MFA TOTP Brute Force Attempts

This rule detects high-frequency failed TOTP code attempts for a single user in a short time span. Such behavior could indicate an adversary attempting to bypass multi-factor authentication (MFA) protections using valid credentials. Understanding the context of the user’s typical behavior and identifying anomalies in the log data are critical to determining the nature of the activity.

Possible Investigation Steps:

Review the Source IP Address: - Check the source.ip or azure.signinlogs.caller_ip_address field. - Determine if the IP address is associated with the user’s typical login locations. - Look for unusual geographic patterns or anomalous IP addresses (e.g., proxies, VPNs, or locations outside the user’s normal activity).

Analyze User Activity: - Identify the user from the azure.signinlogs.properties.sign_in_identifier field. - Determine if the user is currently active from another device or session. Session hijacking could explain parallel activity with failed attempts. - Review past logs for the user to determine whether MFA failures or other anomalies are consistent or new.

Inspect the Authentication Method: - Evaluate the azure.signinlogs.properties.mfa_detail.auth_method field: OATH verification code. - Confirm if the user typically uses TOTP codes or another MFA method (e.g., push notifications). - Verify if there are any recent changes to the user’s MFA settings that may explain multiple failed attempts.

Evaluate the User Agent: - Check the user_agent.original field. - Identify if the user agent matches a typical browser or a potentially malicious script (e.g., Python-based). - Look for deviations in operating system or browser versions from the user’s normal activity.

Analyze Conditional Access Policies: - Review the azure.signinlogs.properties.applied_conditional_access_policies for enforced grant controls. - Verify if MFA failures are tied to legitimate security policies (display_name: Require multifactor authentication for admins).

Correlate with Other Events: - Search for other authentication attempts involving the same azure.signinlogs.caller_ip_address, user_principal_name, or azure.signinlogs.properties.app_id. - Look for suspicious activity patterns, such as password resets, privilege escalation, or account lockouts.

False Positive Analysis:

  • Unintentional User Behavior:
  • Verify if the failed attempts could result from the user’s unfamiliarity with TOTP codes or issues with device synchronization.
  • Check if the user recently switched MFA methods or devices, which could explain multiple failures.
  • Determine if this is whitebox testing or a developer testing MFA integration.
  • Administrative Actions:
  • Determine if the activity is related to legitimate administrative testing or configuration changes in the MFA system.

Response and Remediation:

  • Immediate Actions:
  • If proven malicious, lock the affected account temporarily to prevent further unauthorized attempts.
  • Notify the user of suspicious activity and validate their access to the account.
  • Reset passwords and MFA settings for the affected user to prevent unauthorized access while communicating with the user.
  • Strengthen Authentication Policies:
  • Ensure conditional access policies are configured to monitor and restrict anomalous login behavior.
  • Consider a different MFA method or additional security controls to prevent future bypass attempts.
  • Monitor and Audit:
  • Implement additional monitoring to track high-frequency authentication failures across the environment.
  • Audit historical logs for similar patterns involving other accounts to identify broader threats.
  • Educate and Train Users:
  • Provide guidance on the secure use of MFA and the importance of recognizing and reporting suspicious activity.

Setup

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Required Azure Entra Sign-In Logs

This rule requires the Azure logs integration be enabled and configured to collect all logs, including sign-in logs from Entra. In Entra, sign-in logs must be enabled and streaming to the Event Hub used for the Azure logs integration.

Rule query

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from logs-azure.signinlogs* metadata _id, _version, _index
| where
    // filter for Entra Sign-In Logs
    event.dataset == "azure.signinlogs"
    and azure.signinlogs.operation_name == "Sign-in activity"

    // filter for MFA attempts with OATH conditional access attempts or TOTP
    and azure.signinlogs.properties.authentication_requirement == "multiFactorAuthentication"
    and azure.signinlogs.properties.mfa_detail.auth_method == "OATH verification code"

    // filter on failures only from brute-force attempts
    and azure.signinlogs.properties.conditional_access_status == "failure"
    and azure.signinlogs.result_description == "Authentication failed during strong authentication request."
| keep azure.signinlogs.properties.sign_in_identifier
| stats
    // aggregate by the sign-in account or principal
    failed_totp_code_attempts = count(*) by azure.signinlogs.properties.sign_in_identifier
| where
    // filter on high frequency for a single user
    failed_totp_code_attempts > 30

Framework: MITRE ATT&CKTM

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