The IRS Doc Malware campaign is a low-severity threat primarily leveraging spearphishing attachments to deliver malicious payloads. The attack vector involves sending targeted emails with malicious documents (maldocs) that, when opened, execute embedded scripts. These scripts utilize Windows command-line interfaces and PowerShell to execute further malicious activities. The malware employs scripting techniques to establish persistence on infected systems by modifying registry run keys or placing executables in startup folders. It also uses Background Intelligent Transfer Service (BITS) jobs to facilitate stealthy and reliable data transfer or command and control communications. The malware communicates over commonly used network ports and employs standard cryptographic protocols to encrypt its communications, making detection and analysis more challenging. Although no known exploits in the wild have been reported, the campaign's use of multiple MITRE ATT&CK techniques such as T1193 (Spearphishing Attachment), T1059 (Command-Line Interface), T1086 (PowerShell), T1064 (Scripting), T1060 (Registry Run Keys/Startup Folder), T1197 (BITS Jobs), T1043 (Commonly Used Port), and T1032 (Standard Cryptographic Protocol) indicates a multi-faceted approach to infection, persistence, and communication. The campaign's low severity rating suggests limited impact or scope at the time of reporting, but the use of sophisticated techniques warrants vigilance.

For European organizations, the IRS Doc Malware campaign poses risks primarily related to initial compromise through spearphishing, which can lead to unauthorized access, data exfiltration, and potential lateral movement within networks. The use of PowerShell and scripting can bypass traditional signature-based defenses, increasing the likelihood of successful infection. The persistence mechanisms via registry and startup folders can allow long-term presence on systems, complicating remediation efforts. Encrypted communications over common ports may evade network monitoring tools, potentially allowing attackers to maintain command and control channels undetected. While the campaign's low severity suggests limited immediate damage, targeted attacks on sensitive sectors such as finance, government, or critical infrastructure in Europe could result in confidentiality breaches or operational disruptions. The campaign's stealthy nature and use of legitimate Windows features make detection challenging, increasing the risk of prolonged undetected intrusions.

European organizations should implement targeted defenses against spearphishing and maldoc-based attacks. This includes deploying advanced email filtering solutions capable of detecting malicious attachments and embedded scripts. Endpoint detection and response (EDR) tools should be configured to monitor and alert on suspicious PowerShell activity, command-line executions, and modifications to registry run keys or startup folders. Network monitoring should focus on detecting unusual BITS job creations and encrypted communications over non-standard or commonly used ports. Organizations should enforce strict application whitelisting to prevent unauthorized script execution and regularly audit persistence mechanisms. User training programs must emphasize the risks of opening unsolicited attachments, especially those purporting to be from trusted entities like tax authorities. Incident response plans should include procedures for rapid identification and removal of maldocs and associated persistence artifacts. Finally, maintaining up-to-date backups and system patching, although no specific patches are indicated, will aid in recovery and reduce exploitation risk.