Adversaries may leverage Microsoft Office-based applications for persistence between startups. Microsoft Office is a fairly common application suite on Windows-based operating systems within an enterprise network. There are multiple mechanisms that can be used with Office for persistence when an Office-based application is started; this can include the use of Office Template Macros and add-ins.
A variety of features have been discovered in Outlook that can be abused to obtain persistence, such as Outlook rules, forms, and Home Page.[1] These persistence mechanisms can work within Outlook or be used through Office 365.[2]
| ID | Name | Description |
|---|---|---|
| G0050 | APT32 |
APT32 have replaced Microsoft Outlook's VbaProject.OTM file to install a backdoor macro for persistence.[3][4] |
| G0047 | Gamaredon Group |
Gamaredon Group has inserted malicious macros into existing documents, providing persistence when they are reopened. Gamaredon Group has loaded the group's previously delivered VBA project by relaunching Microsoft Outlook with the |
| ID | Mitigation | Description |
|---|---|---|
| M1040 | Behavior Prevention on Endpoint |
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. [6] |
| M1042 | Disable or Remove Feature or Program |
Follow Office macro security best practices suitable for your environment. Disable Office VBA macros from executing. Disable Office add-ins. If they are required, follow best practices for securing them by requiring them to be signed and disabling user notification for allowing add-ins. For some add-ins types (WLL, VBA) additional mitigation is likely required as disabling add-ins in the Office Trust Center does not disable WLL nor does it prevent VBA code from executing. [7] |
| M1054 | Software Configuration |
For the Office Test method, create the Registry key used to execute it and set the permissions to "Read Control" to prevent easy access to the key without administrator permissions or requiring Privilege Escalation. [8] |
| M1051 | Update Software |
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.[9] 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 KB4011162 which removes the legacy Home Page feature, are applied to systems.[10] |
Collect process execution information including process IDs (PID) and parent process IDs (PPID) and look for abnormal chains of activity resulting from Office processes. Non-standard process execution trees may also indicate suspicious or malicious behavior. If winword.exe is the parent process for suspicious processes and activity relating to other adversarial techniques, then it could indicate that the application was used maliciously.
Many Office-related persistence mechanisms require changes to the Registry and for binaries, files, or scripts to be written to disk or existing files modified to include malicious scripts. Collect events related to Registry key creation and modification for keys that could be used for Office-based persistence.[11][12]
Microsoft has released a PowerShell script to safely gather mail forwarding rules and custom forms in your mail environment as well as steps to interpret the output.[13] SensePost, whose tool Ruler can be used to carry out malicious rules, forms, and Home Page attacks, has released a tool to detect Ruler usage.[14]