The Efimer Trojan is a multifaceted malware strain actively spreading through compromised WordPress websites, malicious torrent files, and targeted email campaigns impersonating legal professionals. Its primary malicious function is to steal cryptocurrency by intercepting and replacing wallet addresses copied to the clipboard, a technique known as clipboard hijacking. Beyond this, Efimer can execute additional malicious scripts, enhancing its persistence and capabilities. Communication with its command-and-control (C2) infrastructure is conducted over the Tor network, which anonymizes traffic and complicates detection and takedown efforts. The Trojan also incorporates brute-force attack capabilities aimed at WordPress sites, attempting to gain unauthorized access by guessing credentials. Additionally, it harvests email addresses from infected systems to expand its distribution via phishing campaigns. The malware has been observed targeting users predominantly in Brazil, India, Spain, Russia, Italy, and Germany from October 2024 through July 2025, impacting over 5,000 users monitored by Kaspersky. The attack vectors leverage common web application vulnerabilities and social engineering, exploiting WordPress’s widespread deployment and the trust users place in email communications from purported legal entities. The use of the Tor network for C2 communication and the combination of multiple infection and propagation methods make Efimer a persistent and evasive threat. Although no specific affected software versions are listed, the brute-force attacks on WordPress suggest exploitation of weak credentials or unpatched installations. The malware’s tactics align with several MITRE ATT&CK techniques, including clipboard data theft (T1115), command execution (T1059.007), phishing (T1566.002), brute forcing (T1110), and use of anonymizing networks (T1571).

For European organizations, Efimer poses a significant risk primarily to entities using WordPress for their web presence, especially those with inadequate security configurations such as weak passwords or outdated plugins. The clipboard hijacking capability threatens the confidentiality and integrity of cryptocurrency transactions, potentially leading to direct financial losses. The Trojan’s ability to execute additional scripts and harvest email addresses increases the risk of lateral movement within networks and further phishing attacks, potentially compromising sensitive corporate data and user credentials. The use of Tor for C2 communication complicates incident response and attribution efforts. Organizations in sectors with high cryptocurrency usage or those relying heavily on WordPress-based websites for business operations are particularly vulnerable. The malware’s distribution via email campaigns impersonating lawyers also raises the risk of successful social engineering attacks against corporate legal departments and clients, potentially leading to data breaches or fraud. Given the targeting of countries including Spain, Italy, and Germany, European organizations in these regions should be especially vigilant. The threat could disrupt business operations, damage reputations, and result in financial losses due to theft and remediation costs.

To mitigate the Efimer Trojan threat, European organizations should implement a layered security approach tailored to the specific tactics used by this malware. First, ensure all WordPress installations are regularly updated, including core software, themes, and plugins, to close known vulnerabilities. Enforce strong, unique passwords and implement multi-factor authentication (MFA) for WordPress admin accounts to prevent brute-force compromises. Deploy web application firewalls (WAFs) configured to detect and block brute-force attempts and suspicious traffic patterns. Monitor clipboard activity on endpoints, particularly for cryptocurrency wallet address changes, using endpoint detection and response (EDR) tools capable of detecting clipboard hijacking behaviors. Enhance email security by deploying advanced anti-phishing solutions that can identify and quarantine emails impersonating trusted entities such as lawyers. Conduct regular user awareness training focused on recognizing phishing attempts and safe handling of email attachments and links. Network monitoring should include detection of Tor traffic, which is uncommon in many corporate environments, to identify potential C2 communications. Implement strict egress filtering and network segmentation to limit malware propagation and data exfiltration. Finally, maintain up-to-date backups and incident response plans to quickly recover from infections and minimize operational impact.