Christmas-Themed LNK Files Used for Malware Delivery

Threat Group: Various Cybercriminal Entities
Threat Type: Malware Delivery via LNK Files
Exploited Vulnerabilities: Abuse of Windows LNK File Functionality
Malware Used: Emotet, Ursnif, Qakbot, IcedID
Threat Score: High (8.5/10) – Due to the deceptive nature of LNK files masquerading as legitimate documents, increased holiday-themed phishing campaigns, and the potential for significant data theft and system compromise.
Last Threat Observation: December 2024

Overview

The holiday season often brings a surge in digital communication, with festive greetings and gifts shared online. Unfortunately, cybercriminals exploit this increased digital activity by distributing malicious files disguised as harmless holiday-themed documents. One notable tactic this year involves malicious LNK (Windows shortcut) files named with festive labels such as "christmas_slab.pdf.lnk." These files, cleverly designed to look like legitimate PDF attachments, trigger malware infections upon execution, making them particularly dangerous in environments where users expect to receive seasonal greetings.

Attackers capitalize on the visual similarity between LNK files and standard documents by embedding harmful scripts that execute the moment recipients click the file. The deception is enhanced by using familiar icons and file extensions crafted to appear as common formats. Additionally, many campaigns have used the SSG delivery method to push these malicious files on a broader scale. This technique bypasses many traditional email filters and security measures, enabling malware delivery methods that include banking Trojans, credential stealers, and remote access tools. The ongoing use of this tactic underscores the need for heightened cybersecurity awareness and advanced email security protocols, especially during high-traffic digital seasons like Christmas.

Key Details

• Delivery Method: Cybercriminals rely heavily on phishing emails, embedding festive-themed malicious LNK files as seemingly legitimate document attachments. Their goal is to exploit seasonal goodwill and users' lowered vigilance during the holidays. The SSG delivery method has also been identified as a key distribution vector.
• Target: Both individual users and organizations are targeted, as attackers seek to maximize their reach by casting a wide net through mass email campaigns.
• Functions:
  • Deception: Files are labeled with festive and familiar names, masking their true malicious intent.
  • Execution: Clicking the LNK file triggers the execution of hidden scripts designed to compromise the user's system.
  • Payload Delivery: Malware variants such as banking Trojans, credential stealers, and remote access tools are commonly delivered.
  • Persistence: The malware often establishes persistence through scheduled tasks or registry modifications.
  • Data Exfiltration: Sensitive information, including financial details, is harvested and transmitted to the attackers.
• Obfuscation: Clever file naming and the use of trusted-looking icons enhance believability. The attackers often hide file extensions, making the malicious files appear as standard documents.

Attack Vectors

Malicious LNK files exploit Windows’ inherent functionality to execute commands with minimal user awareness. Upon being clicked, the shortcut file may invoke system utilities such as PowerShell or cmd.exe to download and run malicious payloads. For example, an LNK file may silently execute a PowerShell command that downloads and installs malware from a remote server. This method allows attackers to bypass basic security measures and initiate sophisticated attack chains. Recent campaigns have also shown attackers leveraging the SSG platform for file distribution, further expanding their reach.

Known Indicators of Compromise (IoCs)

File Hashes:

• MD5: 5e86eb5528e8357fbfa8744f239483ca
• SHA1: d7c7beb8d38fbc65af3e3fa782ad688dd60bd8ef
• SHA256: 8bd210b33340ee5cdd9031370eed472fcc7cae566752e39408f699644daf8494

IP Address (Defanged):

• 17[.]43[.]12[.]31

Mitigation and Prevention

• User Awareness: Conduct awareness training on the dangers of suspicious email attachments, emphasizing caution when handling files with unexpected or festive-themed labels.
• Email Filtering: Implement robust email filters capable of detecting and blocking suspicious file types, including LNK files.
• Antivirus Protection: Ensure antivirus and endpoint protection systems are updated and configured to scan for LNK-based threats.
• Two-Factor Authentication (2FA): Strengthen account protection by enabling 2FA wherever possible.
• Monitor Logs: Regularly inspect system logs for unusual activities, such as unexpected command executions or unauthorized downloads.
• Regular Updates: Apply patches and updates promptly to close known vulnerabilities that attackers could exploit.

Risk Assessment

The risk posed by malicious LNK files disguised as festive-themed PDFs is significant due to their convincing appearance and the increased likelihood of user interaction during the holiday season. These files enable attackers to bypass conventional security measures, allowing them to deploy a wide range of malware that can steal sensitive information, cause financial loss, and compromise organizational systems.

Conclusion

Malicious LNK files continue to be a potent vector for malware distribution. Their success lies in the combination of clever file disguise, technical exploitation, and users’ reduced caution during festive periods. Organizations must maintain strong cybersecurity practices, enhance email security, and educate users on recognizing potential threats, especially during holidays when phishing campaigns are most active.

Sources:

1. Internet Storm Center - Christmas "Gift" Delivered Through SSH
2. Virus Total - christmas_slab.pdf
3. AlienVault - Indicators of Compromise