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T1114.003 Email Forwarding Rule

Adversaries may setup email forwarding rules to collect sensitive information. Adversaries may abuse email forwarding rules to monitor the activities of a victim, steal information, and further gain intelligence on the victim or the victim’s organization to use as part of further exploits or operations.5 Furthermore, email forwarding rules can allow adversaries to maintain persistent access to victim’s emails even after compromised credentials are reset by administrators.2 Most email clients allow users to create inbox rules for various email functions, including forwarding to a different recipient. These rules may be created through a local email application, a web interface, or by command-line interface. Messages can be forwarded to internal or external recipients, and there are no restrictions limiting the extent of this rule. Administrators may also create forwarding rules for user accounts with the same considerations and outcomes.31

Any user or administrator within the organization (or adversary with valid credentials) can create rules to automatically forward all received messages to another recipient, forward emails to different locations based on the sender, and more. Adversaries may also hide the rule by making use of the Microsoft Messaging API (MAPI) to modify the rule properties, making it hidden and not visible from Outlook, OWA or most Exchange Administration tools.2

In some environments, administrators may be able to enable email forwarding rules that operate organization-wide rather than on individual inboxes. For example, Microsoft Exchange supports transport rules that evaluate all mail an organization receives against user-specified conditions, then performs a user-specified action on mail that adheres to those conditions.4 Adversaries that abuse such features may be able to enable forwarding on all or specific mail an organization receives.

Item Value
ID T1114.003
Sub-techniques T1114.001, T1114.002, T1114.003
Tactics TA0009
Platforms Linux, Office Suite, Windows, macOS
Version 1.4
Created 19 February 2020
Last Modified 24 October 2025

Procedure Examples

ID Name Description
G0094 Kimsuky Kimsuky has set auto-forward rules on victim’s e-mail accounts.15
G1004 LAPSUS$ LAPSUS$ has set an Office 365 tenant level mail transport rule to send all mail in and out of the targeted organization to the newly created account.12
G1015 Scattered Spider Scattered Spider has redirected emails notifying users of suspicious account activity.10
G0122 Silent Librarian Silent Librarian has set up auto forwarding rules on compromised e-mail accounts.11
G1033 Star Blizzard Star Blizzard has abused email forwarding rules to monitor the activities of a victim, steal information, and maintain persistent access after compromised credentials are reset.1413

Mitigations

ID Mitigation Description
M1047 Audit Enterprise email solutions have monitoring mechanisms that may include the ability to audit auto-forwarding rules on a regular basis.
M1042 Disable or Remove Feature or Program Consider disabling external email forwarding.6
M1041 Encrypt Sensitive Information Use of encryption provides an added layer of security to sensitive information sent over email. Encryption using public key cryptography requires the adversary to obtain the private certificate along with an encryption key to decrypt messages.
M1060 Out-of-Band Communications Channel Use secure out-of-band authentication methods to verify the authenticity of critical actions initiated via email, such as password resets, financial transactions, or access requests.

References

  1. Apple. (n.d.). Reply to, forward, or redirect emails in Mail on Mac. Retrieved June 22, 2021. ↩

  2. Damian Pfammatter. (2018, September 17). Hidden Inbox Rules in Microsoft Exchange. Retrieved October 12, 2021. ↩↩

  3. McMichael, T.. (2015, June 8). Exchange and Office 365 Mail Forwarding. Retrieved October 8, 2019. ↩

  4. Microsoft. (2023, February 22). Mail flow rules (transport rules) in Exchange Online. Retrieved March 13, 2023. ↩

  5. US-CERT. (2018, March 27). TA18-068A Brute Force Attacks Conducted by Cyber Actors. Retrieved October 2, 2019. ↩

  6. Carr, N., Sellmer, S. (2021, June 14). Behind the scenes of business email compromise: Using cross-domain threat data to disrupt a large BEC campaign. Retrieved June 15, 2021. ↩

  7. Microsoft. (2023, February 22). Manage mail flow rules in Exchange Online. Retrieved March 13, 2023. ↩

  8. Microsoft. (n.d.). Get-InboxRule. Retrieved June 10, 2021. ↩

  9. Tyler Hudak. (2022, December 29). To OOB, or Not to OOB?: Why Out-of-Band Communications are Essential for Incident Response. Retrieved August 30, 2024. ↩

  10. Counter Adversary Operations. (2025, July 2). CrowdStrike Services Observes SCATTERED SPIDER Escalate Attacks Across Industries. Retrieved October 13, 2025. ↩

  11. DOJ. (2018, March 23). U.S. v. Rafatnejad et al . Retrieved February 3, 2021. ↩

  12. MSTIC, DART, M365 Defender. (2022, March 24). DEV-0537 Criminal Actor Targeting Organizations for Data Exfiltration and Destruction. Retrieved May 17, 2022. ↩

  13. CISA, et al. (2023, December 7). Russian FSB Cyber Actor Star Blizzard Continues Worldwide Spear-phishing Campaigns. Retrieved June 13, 2024. ↩

  14. Microsoft Threat Intelligence. (2022, August 15). Disrupting SEABORGIUM’s ongoing phishing operations. Retrieved June 13, 2024. ↩

  15. CISA, FBI, CNMF. (2020, October 27). https://us-cert.cisa.gov/ncas/alerts/aa20-301a. Retrieved November 4, 2020. ↩