Description
Adversaries may abuse Microsoft Outlook forms to obtain persistence on a compromised system. Outlook forms are used as templates for presentation and functionality in Outlook messages. Custom Outlook forms can be created that will execute code when a specifically crafted email is sent by an adversary utilizing the same custom Outlook form.(Citation: SensePost Outlook Forms)
Once malicious forms have been added to the user’s mailbox, they will be loaded when Outlook is started. Malicious forms will execute when an adversary sends a specifically crafted email to the user.(Citation: SensePost Outlook Forms)
Platforms
Mitigations (2)
Update SoftwareM1051
For the Outlook methods, blocking macros may be ineffective as the Visual Basic engine used for these features is separate from the macro scripting engine.(Citation: SensePost Outlook Forms) Microsoft has released patches to try to address each issue. Ensure KB3191938 which blocks Outlook Visual Basic and displays a malicious code warning, KB4011091 which disables custom forms by default, and KB40
Behavior Prevention on EndpointM1040
On Windows 10, enable Attack Surface Reduction (ASR) rules to prevent Office applications from creating child processes and from writing potentially malicious executable content to disk. (Citation: win10_asr)
Associated Software (1)
| ID | Name | Type | Context |
|---|---|---|---|
| S0358 | Ruler | Tool | [Ruler](https://attack.mitre.org/software/S0358) can be used to automate the abuse of Outlook Forms to establish persistence.(Citation: SensePost Rule... |
References
- Fox, C., Vangel, D. (2018, April 22). Detect and Remediate Outlook Rules and Custom Forms Injections Attacks in Office 365. Retrieved February 4, 2019.
- SensePost. (2017, September 21). NotRuler - The opposite of Ruler, provides blue teams with the ability to detect Ruler usage against Exchange. Retrieved February 4, 2019.
- Stalmans, E. (2017, April 28). Outlook Forms and Shells. Retrieved February 4, 2019.
Frequently Asked Questions
What is T1137.003 (Outlook Forms)?
T1137.003 is a MITRE ATT&CK technique named 'Outlook Forms'. It belongs to the Persistence tactic(s). Adversaries may abuse Microsoft Outlook forms to obtain persistence on a compromised system. Outlook forms are used as templates for presentation and functionality in Outlook messages. Custom Outlook...
How can T1137.003 be detected?
Detection of T1137.003 (Outlook Forms) typically involves monitoring system logs, network traffic, and endpoint telemetry. Use SIEM rules, EDR solutions, and behavioral analytics to identify suspicious activity associated with this technique.
What mitigations exist for T1137.003?
There are 2 documented mitigations for T1137.003. Key mitigations include: Update Software, Behavior Prevention on Endpoint.
Which threat groups use T1137.003?
While specific threat group attribution may vary, this technique has been observed in various real-world attacks. Check the MITRE ATT&CK website for the latest threat intelligence.