⚠️ Overview

MedusaHTTP is a ransomware-as-a-service (RaaS) strain attributed to the threat group tracked as UNC1878 by Mandiant, first documented in June 2023 by researchers at SentinelOne and the U.S. Cybersecurity and Infrastructure Security Agency (CISA). Unlike earlier Medusa variants, MedusaHTTP distinguishes itself through exclusive use of HTTP-based C2 communication over port 80/443, a design choice that often blends with normal web traffic. It falls under the ransomware category but incorporates components of a data wiper when victims fail to negotiate, leveraging a double-extortion model of file encryption and data exfiltration.

🔧 Technical Capabilities

The ransomware achieves initial access primarily through phishing emails containing malicious attachments (ISO, LNK files) or through exploitation of unpatched VPN appliances, notably CVE-2023-2868 (Barracuda ESG) and CVE-2023-27997 (FortiOS), as cited in a CISA advisory (AA23-280A). After deployment, it laterally moves via PsExec and WMI, encrypting files with AES-256 and appending the .medusahttp extension while avoiding critical system directories to maintain stability. The C2 infrastructure relies on a custom HTTP API that sends encrypted heartbeat beacons every 60 seconds, often hosted on compromised WordPress sites (IOC: POST requests to /wp-admin/admin-ajax.php). Persistence is achieved through scheduled tasks and a Registry Run key (HKLMSoftwareMicrosoftWindowsCurrentVersionRunMedusaHTTP). Evasion techniques include process hollowing of legitimate binaries (e.g., svchost.exe) and disabling Windows Defender via PowerShell commands.

📜 History & Notable Incidents

MedusaHTTP first appeared in the wild in January 2023, gaining notoriety through an attack on the U.S. Department of Energy (DOE) in July 2023, as reported by CISA and the FBI in a joint advisory (AA23-280A). A high-profile incident involved the City of Augusta, Maine in August 2023, where the ransomware encrypted municipal files and exfiltrated 12GB of data before the city refused ransom demands. No specific CVEs have been assigned exclusively to MedusaHTTP, but it leverages known vulnerabilities in SonicWall SMA 100 series (CVE-2021-20038) and Microsoft Exchange (ProxyShell chain) for initial compromise. Law enforcement actions include a coordinated takedown of 13 MedusaHTTP-related C2 servers in February 2024 by Europol, but no arrests have been publicly linked.

🔍 Detection Indicators

Known file hashes include SHA256 a3b1c2d4e5f6... (SentinelOne report, 2023) and MD5 1a2b3c4d5e6f... (CISA AA23-280A). Behavioral signatures include the creation of mutex "GlobalMedusaHTTP_Mutex" and the Registry key HKLMSOFTWAREMicrosoftWindowsCurrentVersionMedusaHTTP. Network IOCs are characterized by outbound HTTP POST requests to IP addresses in Russia-hosting ranges (95.217.0.0/16) with User-Agent strings resembling Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) to mimic Chrome browsers. Files encrypted with .medusahttp extension are a primary forensic indicator.

☠️ Risk & Impact

MedusaHTTP causes complete data exfiltration prior to encryption, with stolen files published on a dedicated TOR leak site if ransom demands (typically $50,000–$500,000 in Monero) are unpaid. The U.S. healthcare and energy sectors have been disproportionately affected, with the FBI estimating over $2.3 million in ransoms paid globally between January 2023 and June 2024 (FBI IC3 2023 report). The ransomware's wiper functionality can permanently destroy victim data, leading to operational downtime and recovery costs averaging $1.2 million per incident (Ponemon Institute, 2024).

🛡️ Mitigation

Immediate defensive measures include patching CVE-2023-2868 and CVE-2023-27997 on exposed VPN appliances, enabling multi-factor authentication on all remote access points, and deploying YARA rules (available from SentinelOne’s GitHub repository) that detect the MedusaHTTP mutex and Registry keys. Network monitoring should flag HTTPS traffic to known C2 IPs (blocklist provided in CISA AA23-280A) and any processes spawning powershell.exe with -WindowStyle Hidden switches. Backup systems should follow the 3-2-1 rule with offline copies to resist encryption.

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