Researchers have identified a sophisticated phishing campaign that uses LinkedIn private messages to distribute a Remote Access Trojan (RAT) through DLL sideloading techniques. The attack begins with threat actors sending messages to high-value individuals on LinkedIn, leveraging social engineering to build trust and convince victims to download a malicious WinRAR self-extracting archive (SFX). This archive extracts four components: a legitimate open-source PDF reader, a malicious DLL designed to be sideloaded by the PDF reader, a portable executable of the Python interpreter, and a decoy RAR file. When the PDF reader is executed, it loads the malicious DLL, which then drops the Python interpreter onto the victim’s system and creates a Windows Registry Run key to ensure persistence across reboots. The Python interpreter runs Base64-encoded shellcode directly in memory, avoiding disk writes and forensic detection. This shellcode establishes communication with an external command-and-control server, granting attackers persistent remote access and enabling data exfiltration. The use of DLL sideloading—a technique where a legitimate application loads a malicious DLL—helps evade traditional security controls by hiding malicious activity within trusted processes. This campaign highlights the growing trend of exploiting social media platforms, which often lack the security monitoring applied to email, as an attack vector. The campaign is opportunistic and spans multiple sectors and regions, making it difficult to quantify its full scope. The abuse of open-source tools and social media messaging underscores the need for organizations to broaden their security posture beyond traditional email-centric defenses. Historical precedents show that LinkedIn has been previously exploited by nation-state actors and cybercriminals for targeted attacks, emphasizing the platform’s attractiveness for initial access. The campaign’s reliance on legitimate tools and social engineering complicates detection and response efforts.

European organizations face significant risks from this campaign due to the widespread use of LinkedIn among professionals and enterprises across the continent. The attack targets high-value individuals, potentially including executives, IT staff, and other privileged users, increasing the risk of lateral movement and privilege escalation within corporate networks. Successful compromise can lead to persistent remote access, data theft, intellectual property loss, and disruption of business operations. The stealthy nature of DLL sideloading and in-memory execution reduces the likelihood of detection by traditional antivirus and endpoint detection systems, increasing dwell time and potential damage. The use of social media messaging as a delivery vector exploits a blind spot in many organizations’ security monitoring, allowing attackers to bypass email defenses and scale their operations with minimal effort. This can lead to widespread infiltration across sectors such as finance, technology, manufacturing, and government institutions in Europe. Additionally, the campaign’s opportunistic nature means that organizations without robust social media security policies and monitoring are particularly vulnerable. The potential for data exfiltration and persistent control over compromised hosts poses a threat to confidentiality, integrity, and availability of critical systems and sensitive information.

1. Extend security monitoring and threat detection capabilities to include social media platforms, especially LinkedIn private messages, using specialized tools or third-party services that can detect suspicious activity and phishing attempts. 2. Implement strict policies and user training focused on social media security awareness, emphasizing the risks of unsolicited messages and the dangers of downloading and executing files from unknown or untrusted sources. 3. Deploy endpoint detection and response (EDR) solutions capable of identifying DLL sideloading behaviors, anomalous process launches, and in-memory code execution to detect and block malicious activity early. 4. Enforce application whitelisting and restrict execution of unauthorized software, including portable interpreters like Python, to limit the ability of attackers to run arbitrary code. 5. Regularly audit and monitor Windows Registry Run keys and startup items for unauthorized persistence mechanisms. 6. Use network segmentation and least privilege principles to limit lateral movement opportunities if a host is compromised. 7. Employ multi-factor authentication (MFA) and strong access controls on LinkedIn and other social media accounts to reduce the risk of account compromise and impersonation. 8. Collaborate with LinkedIn and other social media providers to report and mitigate malicious accounts and phishing campaigns. 9. Conduct regular threat hunting exercises focused on detecting signs of DLL sideloading and unusual Python interpreter activity. 10. Maintain up-to-date threat intelligence feeds and share information about emerging social media-based phishing campaigns within industry groups and CERTs.