A highly focused and financially motivated ransomware campaign has been systematically targeting organizations across the United States, demonstrating a rapid and destructive operational model that prioritizes speed over subtlety. First identified in early May 2024, the threat, known as Fog ransomware, has shown a distinct preference for specific industries, with incident response data indicating that 80 percent of its victims were educational institutions and the remaining 20 percent were in the recreation sector. This ransomware operates not as a monolithic group but as a variant deployed by affiliate threat actors who follow a remarkably consistent playbook. Their approach is best described as a “smash-and-grab” operation; they infiltrate a network, encrypt critical data as quickly as possible, and demand a ransom without engaging in the more time-consuming tactic of data exfiltration. This singular focus on a swift financial payout, combined with a highly effective infiltration method, makes Fog a formidable and immediate threat to unprepared organizations.
A Singular Point of Entry
The entire Fog ransomware campaign hinges on one alarmingly simple and effective initial access method: the exploitation of compromised Virtual Private Network (VPN) credentials. Forensic evidence from every investigated incident consistently showed that attackers gained entry by logging into victim environments with legitimate, stolen credentials for VPN gateways. This approach successfully breached networks using hardware from at least two different VPN vendors, highlighting a widespread and critical vulnerability in remote access security postures that lack sufficient protection. Rather than exploiting complex software flaws, the attackers simply walked through the digital front door using valid keys. This trend underscores the immense risk associated with unsecured network entry points, as a single compromised account can serve as the gateway for a full-scale ransomware deployment. The campaign’s activity, which was geographically contained within the United States, demonstrates how a straightforward attack vector can be leveraged for maximum impact with minimal effort.
Further analysis confirms that Fog operates as a ransomware variant deployed by affiliates, a distinction that is crucial for understanding the threat landscape. This model separates the developers of the malware from the threat actors who carry out the attacks. While the precise organizational structure remains unconfirmed, the similar attack patterns and procedures observed across multiple incidents suggest a coordinated effort or a shared playbook among the affiliates. Their motivation appears to be purely financial, driving their rapid encryption timeline and the notable absence of data exfiltration. This strategy aims for a quick payout without the added complexity of double-extortion tactics, which involve threatening to leak stolen data. The last documented attack in the investigated cases occurred on May 23, 2024, providing a clear operational window and reinforcing the swift, targeted nature of the campaign, which relies on exploiting the weakest link in the security chain: a single set of credentials.
The Post-Compromise Playbook
Once inside a network, the Fog operators execute a methodical, multi-stage attack that combines common penetration testing tools and techniques to achieve their objectives. After gaining initial access via a compromised VPN account, the attackers immediately work to escalate their privileges and move laterally across the network. A common tactic observed was pass-the-hash activity, which allowed them to compromise powerful administrator accounts. With these elevated credentials, they then established Remote Desktop Protocol (RDP) connections to critical infrastructure, including Windows Servers running Hyper-V and, crucially, Veeam backup systems. In at least one documented case, credential stuffing was used as an alternative method for lateral movement. To execute commands and deploy their tools across the compromised environment, the actors utilized PsExec, while RDP and the Server Message Block (SMB) protocol were used to access specific target systems. In a key preparatory step, they disabled Windows Defender on all targeted servers, effectively removing a primary layer of defense just moments before executing the ransomware payload.
To facilitate their operations, the attackers deployed a specific and highly effective toolkit designed for reconnaissance, lateral movement, and disabling recovery options. This toolkit included network administration tools like SoftPerfect Network Scanner and Advanced Port Scanner, which they used to discover hosts and identify open ports across the victim’s environment. For data discovery, they employed SharpShares v2.3, an open-source tool used to enumerate and identify accessible network shares containing valuable files. Perhaps most strategically, the attackers used Metasploit for reconnaissance against Veeam backup servers and deployed a specialized PowerShell script, Veeam-Get-Creds.ps1, designed to extract stored credentials directly from the Veeam Backup and Replication Credentials Manager. This gave them direct access to the backup infrastructure, allowing them to neutralize the primary means of recovery. This deliberate targeting of backup systems demonstrates a sophisticated understanding of incident response and a calculated effort to maximize the pressure on victims to pay the ransom.
Technical Breakdown of the Payload
A detailed technical examination of the Fog ransomware payload reveals a sophisticated design that incorporates techniques common to other modern ransomware variants. The malware’s execution begins with the creation of a log file named DbgLog.sys in the %AppData% directory, which it uses to track its operational status. During its initialization routine, the ransomware queries the system for hardware information by referencing NTDLL.DLL and using the NtQuerySystemInformation function. This allows it to tailor its resource allocation, such as the number of encryption threads, to the specific system’s capabilities for maximum efficiency. The payload can also be executed with several command-line options, including NOMUTEX to permit concurrent instances, TARGET to specify particular file paths for encryption, and CONSOLE to display its output in a terminal window. This flexibility allows the attackers to adapt their deployment strategy to different environments and operational needs, increasing the likelihood of a successful attack.
The core of the ransomware’s operation is controlled by a central JSON configuration block, which contains all the essential parameters for the attack. This block includes the RSA public key used for file encryption, the file extensions to be appended to encrypted files (commonly .FOG or .FLOCKED), the name of the ransom note file, and a list of specific services to shut down prior to encryption. This last step ensures that all target files are unlocked and accessible for encryption. The file discovery process employs standard Windows APIs, including FindFirstVolume and FindFirstFile, to systematically locate all files on the system. The encryption process itself is highly efficient, utilizing a thread pool that scales from two to sixteen threads based on the system’s processor count. It implements the CryptImportKey and CryptEncrypt functions to perform the encryption before renaming the files with the configured extension and writing the ransom note in each directory, leaving victims with clear instructions on how to pay.
Fortifying Defenses Against an Evolving Threat
As a final, destructive step designed to impede recovery, the Fog ransomware executes the command vssadmin.exe delete shadows /all /quiet, which eradicates all Volume Shadow Copies. These snapshots, a native Windows feature, often provide a last line of defense for restoring files without resorting to full backups. By systematically destroying them, the attackers remove a crucial recovery option, thereby increasing the pressure on the victim organization to pay the ransom. This action, combined with the earlier targeting of Veeam backup systems, illustrates a comprehensive strategy aimed at leaving the victim with no other choice. The entire attack chain, from the initial VPN compromise to the final deletion of shadow copies, is meticulously planned to ensure maximum disruption and financial gain. The technical sophistication of the payload, coupled with the strategic dismantling of recovery mechanisms, solidifies Fog’s position as a dangerous and highly effective ransomware threat.
In response to this emergent threat, the Fog ransomware campaign served as a stark reminder of the critical importance of a defense-in-depth security strategy. The attackers’ success was not predicated on zero-day exploits but on the exploitation of common security gaps, particularly in remote access infrastructure. Therefore, organizations were strongly advised to prioritize securing all VPN gateways and, most importantly, enforcing mandatory multi-factor authentication (MFA) on all remote access points to mitigate the risk of credential compromise. Furthermore, the campaign highlighted the necessity of maintaining secure and immutable off-site or offline backup systems that are segregated from the primary network and thus protected from direct attack. Deploying comprehensive endpoint detection and response (EDR) solutions was also recommended to identify and block the malicious activities characteristic of the post-compromise playbook, such as the use of PsExec and the disabling of security software. Ultimately, the lessons from this campaign underscored that a layered defense, addressing vulnerabilities from the network edge to the endpoint, remained the most effective posture against such calculated attacks.
