Malware

Malware Distribution Through Trusted Microsoft Graph API Channels

Cybersec Sentinel

Mar 12, 2025 • 3 min read

Threat Group: Various Advanced Persistent Threats (APTs)
Threat Type: Malware Distribution, Data Exfiltration, Command-and-Control (C2)
Exploited Vulnerabilities: Microsoft Graph API Abuse
Malware Used: Havoc, FINALDRAFT, BirdyClient, Bluelight, Graphite, Graphican, SiestaGraph
Threat Score: High (8.7/10) – Exploitation of trusted Microsoft services, advanced obfuscation, widespread potential data breaches.
Last Threat Observation: March 12, 2025

Overview

In the past 24 hours, a significant cybersecurity threat has emerged involving the exploitation of vulnerabilities in Microsoft's Graph API. Attackers leverage this trusted API to distribute malware, enabling unauthorized access to sensitive data, covert command-and-control (C2) communications, and advanced persistent threats against corporate environments.

Key Details

Delivery Method:

Phishing Emails (HTML attachments with PowerShell commands)
Device Code Phishing (fake meeting invitations)
OAuth vulnerabilities exploitation

Target:

Microsoft 365 environments
Enterprises handling sensitive data

Functions:

Unauthorized data access and exfiltration
Command-and-control via Outlook drafts and OneDrive
Malware distribution through trusted Microsoft services
Lateral movement within compromised networks
System compromise through malware deployment

Obfuscation:

Legitimate Graph API usage masking malicious activities
AES-256 CTR encryption for malware concealment
Exploitation of trusted Microsoft cloud services for covert operations

Attack Vectors

Threat actors exploit the Microsoft Graph API to bypass traditional security measures. Attack methods include phishing emails prompting malicious PowerShell commands, device code phishing to steal credentials, and OAuth token misuse. Additionally, malware utilizes Outlook email drafts and cloud services like OneDrive to maintain covert command-and-control channels, significantly complicating detection efforts.

Exploitation for Command-and-Control (C2)

Malware such as FINALDRAFT exploits Outlook email drafts for covert communication. Commands and responses are embedded in unsent email drafts, evading standard detection methods.

Phishing Techniques

ClickFix Attacks: Users are tricked into executing malicious PowerShell commands from phishing emails disguised as legitimate error messages.
Device Code Phishing: Victims are deceived by fraudulent online meeting invitations containing malicious device codes, granting attackers unauthorized account access.

Data Exfiltration via Trusted Services

Attackers increasingly utilize OneDrive for undetected data exfiltration. By leveraging Graph API control over cloud storage, attackers blend malicious data transfers with legitimate activities, significantly hindering detection.

Logging Bypass Vulnerability

A previously patched vulnerability allowed attackers to evade logging during password spray attacks by altering authentication endpoints. Despite being addressed, it underscores the importance of continuous vigilance and patching.

Known Indicators of Compromise (IoCs)

File Hashes (SHA256):

51796effe230d9eca8ec33eb17de9c27e9e96ab52e788e3a9965528be2902330
989f58c86343704f143c0d9e16893fad98843b932740b113e8b2f8376859d2dd
cc151456cf143c0d9e16893fad98843b932740b113e8b2f8376859d2dd

Domains:

hao771[.]sharepoint.com

Malware Specific Activity:

Bluelight: Exploits CVE-2021-40444, utilizes Graph API via OneDrive for C2.
BirdyClient: Uses OneDrive via Graph API; involves vxdiff.dll and apoint.exe processes.
Siesta: Employs DoorMe backdoor, long sleep timers, .NET library instead of native Graph API calls.
INALDRAFT: Manipulates Outlook drafts, monitors registry keys, and leverages WinrsHost.exe for lateral movement.

Mitigation and Prevention

User Awareness:

Regular training on phishing recognition, secure handling of email attachments, and safe PowerShell practices.

Email Filtering:

Advanced filters targeting malicious HTML attachments and unusual PowerShell commands.

Antivirus Protection:

Endpoint protection solutions monitoring Graph API activity and script execution.

Two-Factor Authentication (2FA):

Mandatory multi-factor authentication for all Graph API access.

Monitor Logs:

Enhanced API logging for OneDrive, Outlook drafts, and OAuth authorization events.

Regular Updates:

Timely patching of Graph API vulnerabilities and adherence to Microsoft's recommended security practices.

Risk Assessment

The Graph API exploitation significantly increases the risk of large-scale data breaches, system compromise, and extensive lateral movement within affected organizations. The threat's stealthy nature and integration with legitimate Microsoft cloud services drastically complicate detection, potentially resulting in substantial financial, operational, and reputational damage.

Resources and Tools for Mitigation

Microsoft Graph Security API: Monitors security alerts, incidents, and threat indicators.
Microsoft Defender for Endpoint: Detects and blocks Graph API exploitation attempts.
Azure API Management: Implements policies to mitigate common API threats.
SIEM Solutions: Facilitates rapid detection and response through comprehensive log analysis.
Threat Intelligence Platforms: Provides actionable insights into emerging threats.

Conclusion

Organizations must implement proactive security measures, enhance employee awareness, and consistently monitor and patch Microsoft Graph API vulnerabilities. Adopting zero-trust principles, proactive threat detection tools, and stringent API access management is crucial in combating this sophisticated and evolving threat.