Outlook Forms
Outlook Forms [T1137.003]
Information
Introduction
Outlook Forms (MITRE ATT&CK ID: T1137.003) is a sub-technique within the MITRE ATT&CK framework under the parent technique "Office Application Startup." This technique involves adversaries abusing Microsoft Outlook forms, which are customizable templates used to display, input, and manage information. Attackers can leverage custom Outlook forms containing malicious scripts or code to execute arbitrary commands, achieve persistence, and compromise targeted systems. Outlook Forms provide a stealthy method of persistence and execution, as they blend into normal user workflows and can evade standard detection mechanisms.
Deep Dive Into Technique
Outlook Forms are customizable interfaces within Microsoft Outlook that allow users to define how information is presented and interacted with. These forms support scripting capabilities, typically via VBScript, enabling adversaries to execute arbitrary commands or scripts when the form is loaded or interacted with.
Technical details and execution methods include:
Form Customization and Creation:
Attackers create or modify Outlook forms (.oft files) to include malicious scripts.
Forms can be embedded directly within emails or stored locally within Outlook folders.
Malicious scripts embedded into forms are typically written in VBScript, providing attackers with powerful scripting capabilities.
Delivery and Execution:
Malicious Outlook forms can be delivered via phishing emails or placed directly into the user's Outlook mailbox by an attacker with prior access.
When the user opens or interacts with a malicious form, embedded scripts execute automatically.
Scripts may execute commands, download payloads, or establish persistence by modifying Outlook configuration or registry settings.
Persistence Mechanisms:
Outlook forms can be installed into user mailboxes, folders, or organizational forms libraries, ensuring persistence across Outlook restarts.
Forms stored in the user’s mailbox or public folders remain persistent and execute scripts upon user interaction or Outlook startup.
Attackers may leverage registry keys such as
HKCU\Software\Microsoft\Office\[version]\Outlook\Formsto register malicious forms for persistence.
Obfuscation and Evasion:
Malicious scripts embedded in Outlook forms may be obfuscated to evade detection by antivirus and endpoint protection solutions.
Outlook forms blend well with legitimate workflows, reducing suspicion and increasing the likelihood of successful execution.
When this Technique is Usually Used
This sub-technique typically appears in various attack scenarios and stages, such as:
Initial Access:
Attackers may deliver malicious Outlook forms through phishing campaigns, tricking users into opening forms embedded in email attachments or links.
Persistence:
Outlook forms serve as a stealthy persistence mechanism, ensuring attackers maintain access to compromised environments even after system reboots or user logoffs.
Execution:
Attackers leverage embedded scripts within Outlook forms to execute arbitrary commands, download additional payloads, or perform reconnaissance activities.
Credential Harvesting and Information Theft:
Malicious scripts within Outlook forms may collect sensitive information, credentials, or emails and exfiltrate data to attacker-controlled servers.
Lateral Movement and Privilege Escalation:
Once initial access is gained, attackers may use Outlook forms to execute scripts that facilitate lateral movement or privilege escalation within the compromised environment.
How this Technique is Usually Detected
Detection methods, tools, and Indicators of Compromise (IoCs) include:
Monitoring Outlook Form Registrations:
Regularly auditing Outlook form installations and registrations stored in registry keys (
HKCU\Software\Microsoft\Office\[version]\Outlook\Forms) or within Outlook folders and organizational forms libraries.
Endpoint Detection and Response (EDR) Tools:
Using EDR solutions to detect unusual scripting activities originating from Outlook processes (e.g.,
OUTLOOK.EXE) or suspicious VBScript execution.
Behavioral Analysis:
Monitoring Outlook processes for abnormal behaviors, including unexpected script execution, network connections, file downloads, or modifications to system configurations.
Email Gateway and Content Filtering Solutions:
Implementing email security gateways capable of inspecting and blocking malicious Outlook form attachments (.oft files) or emails containing embedded forms with suspicious scripts.
Registry and File System Auditing:
Monitoring registry and file system changes related to Outlook forms, including unauthorized form installations or modifications.
Specific Indicators of Compromise (IoCs):
Presence of unknown or suspicious
.oftfiles within user mailboxes or Outlook folders.Unusual registry entries related to Outlook form registration.
Suspicious outbound network connections initiated by Outlook processes.
Detection of obfuscated VBScript or PowerShell scripts embedded within Outlook form files.
Why it is Important to Detect This Technique
Detecting the usage of malicious Outlook Forms is crucial due to the following potential impacts on systems and networks:
Persistence and Long-term Compromise:
Attackers can leverage Outlook forms as a persistent foothold, maintaining access to compromised systems over prolonged periods, even after reboots or user logoffs.
Stealth and Evasion:
Outlook forms blend seamlessly with legitimate workflows, making detection challenging and enabling attackers to evade traditional antivirus and security mechanisms.
Data Exfiltration and Information Theft:
Malicious scripts embedded within Outlook forms can silently harvest sensitive emails, credentials, and confidential information, leading to data breaches and compliance violations.
Execution of Malicious Payloads:
Outlook forms may execute arbitrary commands or scripts, potentially downloading and executing secondary payloads, ransomware, or remote access tools (RATs).
Facilitation of Further Attacks:
Once established, attackers may leverage compromised Outlook forms to conduct lateral movement, privilege escalation, and network reconnaissance, significantly increasing the scope and severity of an incident.
Early detection of malicious Outlook forms is critical to minimize these risks, prevent prolonged compromises, and reduce potential damage to organizational assets and reputation.
Examples
Real-world examples demonstrating the use and impact of malicious Outlook Forms include:
APT32 (OceanLotus) Campaign:
Attackers leveraged custom Outlook forms embedded in phishing emails containing malicious VBScript code.
Upon opening, the forms executed scripts to download and execute additional malware payloads, enabling persistent access and data exfiltration from targeted organizations.
FIN7 Group Attacks:
FIN7 utilized customized Outlook forms containing embedded scripts to gather credentials and sensitive information from targeted corporate mailboxes.
Malicious scripts executed upon user interaction, silently exfiltrating data to attacker-controlled infrastructure, enabling further compromise and financial fraud.
Phishing Campaigns Targeting Financial Institutions:
Attackers distributed phishing emails containing malicious Outlook forms designed to execute scripts upon opening.
Scripts collected sensitive banking credentials and financial information, leading to significant financial losses and operational disruptions.
Targeted Espionage Operations:
Nation-state actors have reportedly used customized Outlook forms embedded with scripts to silently gather sensitive intelligence information from government agencies and defense contractors.
Forms executed scripts upon user interaction, exfiltrating sensitive emails and documents to attacker-controlled servers.
These examples illustrate the significant threat posed by malicious Outlook Forms, highlighting the importance of robust detection, prevention, and response capabilities to mitigate associated risks.
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