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CISA, FBI Issue Alert Over Rising Interlock Ransomware Attacks on Critical Infrastructure

 

The Cybersecurity and Infrastructure Security Agency (CISA) and the Federal Bureau of Investigation (FBI) have raised an alarm over an increase in ransomware activity linked to the Interlock gang. The advisory, released on Tuesday in collaboration with the Department of Health and Human Services (HHS) and the Multi-State Information Sharing and Analysis Center (MS-ISAC), warns that the group is actively targeting businesses and critical infrastructure in double extortion attacks.

The alert includes indicators of compromise (IOCs) gathered from recent investigations—some as recent as June 2025—and outlines protective measures for network defenders.

Emerging in September 2024, Interlock is a relatively new but rapidly growing ransomware operation. It has launched attacks across various global sectors, with a particular focus on healthcare. The gang has previously been connected to ClickFix intrusions, where they impersonated IT utilities to breach networks, and to malware campaigns using a remote access trojan (RAT) known as NodeSnake, particularly affecting U.K. universities.

The group recently claimed responsibility for cyberattacks on DaVita, a Fortune 500 kidney care company, leaking 1.5 terabytes of stolen data, and Kettering Health, a major healthcare provider with over 120 outpatient locations and more than 15,000 employees.

According to the FBI, the Interlock gang has been observed using unusual methods to infiltrate systems.

"FBI observed actors obtaining initial access via drive-by download from compromised legitimate websites, which is an uncommon method among ransomware groups," the advisory notes.

The gang uses a double extortion model—first stealing and then encrypting victims’ data—forcing organizations to pay not just to restore systems but also to prevent public data leaks.

Interlock RAT Evolves in New KongTuke Web-Inject Attacks Targeting U.S. Industries

 

A recently enhanced version of the Interlock remote access Trojan (RAT) is being deployed in an ongoing web-inject campaign linked to the ransomware group behind it. Known for its double-extortion tactics, Interlock has now shifted its technical approach with a more covert RAT variant written in PHP. According to a new report by The DFIR Report, this marks a significant advancement in the group’s capabilities and strategy.  

Interlock first emerged in late 2024, attacking high-profile targets such as Texas Tech University’s Health Sciences Centers. Earlier this year, cybersecurity firm Quorum Cyber detailed two versions of the group’s malware, named NodeSnake, focused on maintaining persistence and exfiltrating data. The newest version introduces additional stealth features, most notably a transition from JavaScript to PHP, allowing the malware to blend more easily with normal web traffic and avoid detection. 

This enhanced RAT is tied to a broader web-inject threat campaign dubbed “KongTuke,” where victims are tricked into running malicious scripts after visiting compromised websites. Visitors encounter what appears to be a legitimate CAPTCHA but are actually prompted to paste dangerous PowerShell commands into their systems. This action initiates the Interlock RAT, giving attackers access to the machine. 

Once activated, the malware gathers extensive data on the infected system. Using PowerShell, it collects system information, running processes, mounted drives, network connections, and checks its own privilege level. This enables attackers to evaluate the environment quickly and plan further intrusion tactics. It then connects back to command-and-control infrastructure, leveraging services like Cloudflare Tunneling for stealthy communication. Remote desktop protocol (RDP) is used for lateral movement and persistent access. 

Researchers say the targeting in this campaign appears opportunistic, not industry-specific. Victims across various sectors in the U.S. have been identified, with the attackers casting a wide net and focusing efforts where systems and data seem valuable or more vulnerable.  

Defensive recommendations from experts include improving phishing awareness, restricting the use of the Windows Run dialog box, enforcing least privilege access, and requiring multifactor authentication. Blocking unnecessary use of RDP is also essential. 

The growing sophistication of the Interlock RAT and its integration into mass web-inject campaigns reflects an evolving cyber threat landscape where stealth, automation, and social engineering play a central role.

‘FileFix’ Malware Trick Amplifies Interlock Ransomware Threat With Evolved Attack Tactic

 

Cybersecurity researchers have identified a dangerous new twist to the notorious ClickFix malware tactic. The evolved variant—called FileFix—is now being weaponized in active ransomware campaigns, further advancing the threat landscape.

ClickFix typically lures users by showing them a bogus issue—like a fake CAPTCHA or a misleading virus alert—and then offers a “solution” that involves copying and pasting a command from a compromised website into the Windows Run dialog. This command often triggers the download and execution of malicious software.

However, the new FileFix technique modifies that approach. Instead of using the Run command, it instructs users to paste a string into the File Explorer address bar. Though it appears as a legitimate file path, the string is actually a disguised PowerShell command, cleverly masked using comment syntax.

In recent attacks observed in the wild, executing this PowerShell string installs a PHP-based version of the Interlock Remote Access Trojan (RAT). Once active, the RAT performs a range of actions—scanning system and network configurations, identifying backup systems, navigating through local file directories, probing Active Directory environments, and even inspecting domain controllers.

Eventually, the RAT leads to the deployment of the Interlock ransomware encryptor.

Interlock first appeared in September 2024 and was publicly detected by November the same year. It stood out by targeting both Windows and FreeBSD systems. Some high-profile victims include Wayne County (Michigan), Texas Tech University Health Sciences Center, Heritage Bank & McCormick–Priore, and Kettering Health.

The ransomware employs the typical double extortion approach—stealing sensitive data before locking systems with encryption to demand ransom.

As of mid-2025, Interlock has been linked to at least 14 confirmed incidents, with healthcare entities making up about one-third of the total. This shift in delivery method suggests active development of the malware and underscores its ongoing threat to global organizations.

Kettering Health Ransomware Attack Linked to Interlock Group

 

Kettering Health, a prominent healthcare network based in Ohio, is still grappling with the aftermath of a disruptive ransomware attack that forced the organization to shut down its computer systems. The cyberattack, which occurred in mid-May 2025, affected operations across its hospitals, clinics, and medical centers. Now, two weeks later, the ransomware gang Interlock has officially taken responsibility for the breach, claiming to have exfiltrated more than 940 gigabytes of data.  

Interlock, an emerging cybercriminal group active since September 2024, has increasingly focused on targeting U.S.-based healthcare providers. When CNN first reported on the incident on May 20, Interlock had not yet confirmed its role, suggesting that ransom negotiations may have been in progress. With the group now openly taking credit and releasing some of the stolen data on its dark web site, it appears those negotiations either failed or stalled. 

Kettering Health has maintained a firm position that they are against paying ransoms. John Weimer, senior vice president of emergency operations, previously stated that no ransom had been paid. Despite this, the data breach appears extensive. Information shared by Interlock indicates that sensitive files were accessed, including private patient records and internal documents. Patient information such as names, identification numbers, medical histories, medications, and mental health notes were among the compromised data. 

The breach also impacted employee data, with files from shared network drives also exposed. One particularly concerning element involves files tied to Kettering Health’s in-house police department. Some documents reportedly include background checks, polygraph results, and personally identifiable details of law enforcement staff—raising serious privacy and safety concerns. In a recent public update, Kettering Health announced a key development in its recovery process. 

The organization confirmed it had restored core functionalities of its electronic health record (EHR) system, which is provided by healthcare technology firm Epic. Officials described this restoration as a significant step toward resuming normal operations, allowing teams to access patient records, coordinate care, and communicate effectively across departments once again. The full scope of the breach and the long-term consequences for affected individuals still remains uncertain. 

Meanwhile, Kettering Health has yet to comment on whether Interlock’s claims are fully accurate. The healthcare system is working closely with cybersecurity professionals and law enforcement agencies to assess the extent of the intrusion and prevent further damage.

Interlock Ransomware Gang Deploys ClickFix Attacks to Breach Corporate Networks

 

Cybersecurity researchers have revealed that the Interlock ransomware gang has adopted a deceptive social engineering technique called ClickFix to infiltrate corporate networks. This method involves tricking users into executing malicious PowerShell commands under the guise of resolving system errors or completing identity verification steps, leading to the deployment of file-encrypting malware. 

While ClickFix attacks have previously been associated with ransomware campaigns, this marks the first confirmed use by Interlock, a ransomware operation that surfaced in late September 2024. The group targets both Windows systems and FreeBSD servers and maintains a dark web leak portal to pressure victims into paying ransoms that can reach millions of dollars. Interlock does not seem to operate as a ransomware-as-a-service (RaaS) model. 

According to Sekoia researchers, Interlock began using ClickFix tactics in January 2025. Attackers set up fake websites mimicking legitimate IT tools—such as Microsoft Teams and Advanced IP Scanner—to lure victims. These fake sites prompt users to click a “Fix it” button, which silently copies a malicious PowerShell script to the user’s clipboard. If run, the command downloads a 36MB PyInstaller payload that installs malware under the guise of a legitimate tool. 

Researchers found the malicious campaign hosted on spoofed domains like microsoft-msteams[.]com, microstteams[.]com, ecologilives[.]com, and advanceipscaner[.]com. Only the last domain led to the actual malware dropper disguised as Advanced IP Scanner. When users unknowingly run the script, a hidden PowerShell window executes actions such as system reconnaissance, persistence via Windows Registry, and data exfiltration. The attackers deploy a range of malware via command-and-control (C2) servers, including LummaStealer, BerserkStealer, keyloggers, and the Interlock RAT—a basic remote access trojan capable of dynamic configuration, file exfiltration, shell command execution, and DLL injection. 

Post-compromise, Interlock operators use stolen credentials to move laterally through networks via RDP, leveraging remote access tools like PuTTY, AnyDesk, and LogMeIn. Data is exfiltrated to Azure Blob Storage, after which the Windows variant of Interlock ransomware is scheduled to run daily at 8:00 PM—a redundancy tactic to ensure encryption if the initial payload fails. The gang’s ransom notes have also evolved, now placing emphasis on the legal and regulatory consequences of leaked data. 

ClickFix attacks are gaining popularity among various cybercriminal groups, with recent reports also linking them to North Korean state-sponsored actors like the Lazarus Group, who use similar tactics to target job seekers in the cryptocurrency sector.

Interlock Ransomware: New Threat Targeting FreeBSD Servers and Critical Infrastructure Worldwide

 

The Interlock ransomware operation, launched in late September 2024, is increasingly targeting organizations around the globe. Distinctly, this new threat employs an encryptor specifically designed to attack FreeBSD servers, a relatively uncommon tactic among ransomware groups.

Interlock has already affected six organizations and publicly leaked stolen data after ransoms went unpaid. One prominent victim, Wayne County in Michigan, experienced a cyberattack early in October, adding to the list of affected entities.

Details about Interlock remain limited, with early reports emerging from cybersecurity responder Simo in October. Simo's analysis noted a new backdoor associated with the ransomware, discovered during an investigation on VirusTotal.

Shortly after, MalwareHunterTeam identified a Linux ELF encryptor related to Interlock. Upon further examination, BleepingComputer confirmed that this executable was built specifically for FreeBSD 10.4, though attempts to execute it in a FreeBSD environment failed.

Although ransomware targeting Linux-based VMware ESXi servers is common, an encryptor for FreeBSD is rare. The now-defunct Hive ransomware, disrupted by the FBI in 2023, was the only other known operation with a FreeBSD encryptor.

Trend Micro researchers shared additional samples of the Interlock FreeBSD ELF encryptor and a Windows variant, noting that FreeBSD is often used in critical infrastructure. This likely makes it a strategic target for Interlock, as attacks on these systems can lead to significant service disruptions.

Trend Micro emphasizes that Interlock’s focus on FreeBSD infrastructure allows attackers to disrupt essential services and demand high ransoms, as these systems are integral to many organizations’ operations.

It is important to note that Interlock ransomware is unrelated to any cryptocurrency token of the same name.

While BleepingComputer encountered issues with running the FreeBSD encryptor, they successfully tested the Windows version, which performed actions like clearing event logs and deleting the main binary using rundll32.exe if self-deletion is enabled.

When encrypting files, Interlock appends the .interlock extension and generates a ransom note titled "!README!.txt" in each affected folder. The note explains the encryption, threats, and includes links to a Tor-based negotiation site where victims can communicate with the attackers. Each victim receives a unique ID and email for registration on this negotiation platform.

During attacks, Interlock breaches networks, steals sensitive data, and then deploys the encryptor to lock down files. The data theft supports a double-extortion scheme, with threats to leak data if ransoms—ranging from hundreds of thousands to millions of dollars—are not paid.