MalwarePublished 14 Jul 2025

KongTuke FileFix Leads to New Interlock RAT Variant

Source Reddit NetSec

Description

Researchers from The DFIR Report, in partnership with Proofpoint, have identified a new and resilient variant of the Interlock ransomware group’s remote access trojan (RAT). This new malware, a shift from the previously identified JavaScript-based [Interlock RAT](https://blog.sekoia.io/interlock-ransomware-evolving-under-the-radar/) (aka [NodeSnake](https://www.quorumcyber.com/wp-content/uploads/2025/06/20250416-Higher-Education-Sector-RAT.pdf)), uses PHP and is being used in a widespread campaign.

Impact

For European organizations, the emergence of a PHP-based Interlock RAT variant poses significant risks, especially for entities relying on PHP-driven web infrastructure such as content management systems, e-commerce platforms, and custom web applications. Successful compromise could lead to unauthorized access to sensitive data, disruption of critical services, and potential ransomware deployment resulting in operational downtime and financial losses. The RAT's remote access capabilities facilitate stealthy persistence and lateral movement, increasing the likelihood of widespread network compromise. Given Europe's stringent data protection regulations like GDPR, breaches involving personal or sensitive data could result in severe legal and reputational consequences. Additionally, sectors with high-value targets such as finance, healthcare, and government institutions may face elevated threats due to the strategic value of their data and services. The campaign's widespread nature indicates a broad targeting approach, which could impact organizations of varying sizes and industries across Europe.

Defensive guidance

European organizations should implement targeted defenses focusing on PHP environments. This includes rigorous patch management for all PHP applications and underlying web servers to close known vulnerabilities that could be exploited to deploy the RAT. Employing web application firewalls (WAFs) with updated signatures can help detect and block malicious PHP payloads and command-and-control traffic. Network segmentation should be enforced to limit lateral movement if a breach occurs. Continuous monitoring for unusual PHP script executions, especially those initiating outbound connections, can provide early detection of RAT activity. Endpoint detection and response (EDR) solutions should be tuned to identify behaviors consistent with remote access trojans, including persistence mechanisms and anomalous network communications. Organizations should also conduct regular security audits and penetration testing focused on web application security. User awareness training should emphasize phishing and social engineering tactics that may be used to deliver the initial payload. Finally, incident response plans must be updated to address ransomware scenarios linked to RAT infections, ensuring rapid containment and recovery.

Summary

The KongTuke FileFix represents a newly identified variant of the Interlock ransomware group's remote access trojan (RAT) family. Previously, the Interlock RAT, also known as NodeSnake, was primarily JavaScript-based. This new variant marks a significant evolution by utilizing PHP as its core language, which may enhance its stealth and persistence capabilities within compromised environments. The malware is part of a widespread campaign, indicating active and ongoing exploitation attempts. The shift to PHP suggests attackers are targeting web server environments or applications that support PHP, potentially broadening the attack surface compared to the earlier JavaScript variant. This RAT likely facilitates unauthorized remote access, enabling attackers to perform reconnaissance, lateral movement, data exfiltration, and potentially deploy ransomware payloads. Although no specific affected software versions or exploits have been identified, the campaign's scale and the malware's adaptability underscore a persistent threat. The technical details sourced from a Reddit NetSec post and The DFIR Report, in partnership with Proofpoint, lend credibility to the findings despite minimal discussion levels. The absence of known exploits in the wild suggests this variant is either newly deployed or under active development, but its association with a ransomware group elevates its risk profile.

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Description

AI analysisMachine-generated, updated 15 Aug 2025, 00:33 UTC

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