https://feed.craftedsignal.io/tags/exchange/Trending threats, MITRE ATT&CK coverage, and detection metadata — refreshed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioWed, 03 Jan 2024 12:00:00 +0000https://feed.craftedsignal.io/briefs/2024-01-activesync-device-added/Wed, 03 Jan 2024 12:00:00 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2024-01-activesync-device-added/The rule detects the use of the Exchange PowerShell cmdlet, Set-CASMailbox, to add a new ActiveSync allowed device, potentially allowing attackers to gain persistent access to sensitive email data by adding unauthorized devices.This detection identifies the use of the Exchange PowerShell cmdlet, Set-CASMailbox, to add a new ActiveSync allowed device. Attackers may target user email to collect sensitive information by adding unauthorized devices to a user’s allowed ActiveSync devices. The rule focuses on detecting suspicious PowerShell activity by monitoring for specific command patterns indicative of unauthorized device additions. This activity can lead to persistent access to sensitive email data, bypassing normal authentication controls. The original Elastic detection rule was created on 2020/12/15 and updated on 2026/05/04. This matters for defenders because it highlights a persistence mechanism that can be difficult to detect through traditional means.

Attack Chain

1. An attacker gains initial access to a privileged account with Exchange management permissions.
2. The attacker uses PowerShell to execute the Set-CASMailbox cmdlet.
3. The attacker modifies the ActiveSyncAllowedDeviceIDs attribute for a target user’s mailbox.
4. The attacker adds a rogue device ID to the list of allowed devices.
5. The attacker configures a mobile device with the rogue device ID to synchronize with the target mailbox.
6. The attacker gains persistent access to the target user’s email, calendar, and contacts.
7. The attacker exfiltrates sensitive data from the mailbox.
8. The attacker maintains persistence even after password changes by continuing to synchronize via the added device.

Impact

Successful exploitation could lead to unauthorized access to sensitive email data, including confidential communications, financial information, and personal data. This can result in data breaches, compliance violations, and reputational damage. The scope of the impact depends on the privileges of the compromised account and the sensitivity of the data contained in the targeted mailboxes.

Recommendation

• Deploy the Sigma rule ActiveSyncAllowedDeviceID Added via PowerShell to your SIEM and tune for your environment to detect suspicious activity.
• Enable Sysmon process-creation logging to capture PowerShell commands for the rule above.
• Review Exchange audit logs for instances of Set-CASMailbox being used to modify ActiveSyncAllowedDeviceIDs.
• Implement multi-factor authentication (MFA) for all accounts, especially those with Exchange management privileges.
• Regularly audit ActiveSync device configurations to identify unauthorized devices.

]]>mediumadvisoryexchangeactivesyncpowershellpersistencehttps://feed.craftedsignal.io/briefs/2024-01-exchange-mailbox-export/Wed, 03 Jan 2024 12:00:00 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2024-01-exchange-mailbox-export/Adversaries may use the New-MailboxExportRequest PowerShell cmdlet to export mailboxes in Exchange, potentially leading to sensitive information theft.Attackers may target user email to collect sensitive information. The New-MailBoxExportRequest cmdlet is used to export the contents of a primary mailbox or archive to a .pst file. Note that this is done on a per-mailbox basis and this cmdlet is available only in on-premises Exchange. Attackers can abuse this functionality in preparation for exfiltrating contents, which is likely to contain sensitive and strategic data. This activity is typically performed using PowerShell or similar scripting tools and can be difficult to detect without specific monitoring in place. The activity may be part of a larger attack campaign targeting sensitive information.

Attack Chain

1. An attacker gains initial access to a compromised system with sufficient privileges to access Exchange PowerShell.
2. The attacker authenticates to the Exchange server using PowerShell.
3. The attacker uses the New-MailboxExportRequest cmdlet to initiate the export of a target mailbox to a .pst file. The command may include parameters to filter specific content.
4. The Exchange server processes the export request, creating a .pst file containing the mailbox data.
5. The attacker retrieves the exported .pst file from the designated file path.
6. The attacker may compress and archive the .pst file to reduce its size for exfiltration.
7. The attacker exfiltrates the .pst file to an external location controlled by the attacker.
8. The attacker analyzes the .pst file to extract sensitive information such as credentials, financial data, or intellectual property.

Impact

Successful exploitation allows the attacker to gain access to sensitive information contained within the exported mailboxes. This could lead to financial loss, reputational damage, or compromise of intellectual property. Depending on the scope of the export requests, multiple mailboxes may be compromised, impacting a large number of users. The impact is significant because email often contains highly sensitive business communications and data.

Recommendation

• Enable Sysmon process creation logging to monitor PowerShell execution with command-line arguments (Data Source: Sysmon).
• Implement the provided Sigma rule to detect the use of New-MailboxExportRequest cmdlet in PowerShell commands.
• Review the privileges of users with the “Mailbox Import Export” privilege to ensure that the least privilege principle is being followed.
• Monitor Windows Security Event Logs for PowerShell activity related to mailbox export requests (Data Source: Windows Security Event Logs).
• Investigate any alerts generated by the Sigma rules to identify potential malicious activity.

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