Forensic Dissection of the .hamster15 Ransomware Attack: Inside the MedusaLocker Architecture

When an enterprise network is suddenly paralyzed and system administrators find their critical assets renamed with unconventional, iterative extensions like .hamster15, .hamster20, or .hamster50, the confusion is immediate. The whimsical naming convention heavily contrasts with the devastating reality of the attack. Through extensive code decomposition and forensic telemetry, Lockbit Decryptor Lab engineers have definitively linked this “Hamster” campaign to the notorious MedusaLocker Ransomware-as-a-Service (RaaS) syndicate.

MedusaLocker, first surfacing in late 2019, operates on an affiliate model. The core developers write and maintain the highly efficient encryption engine, while disparate affiliate groups distribute the payload. The iterative numerical suffixes (15, 20, 30, 40) attached to the “hamster” root are distinct affiliate tracking markers, allowing the core developers to attribute ransom payments to specific attack campaigns.

This malware is incredibly aggressive. Before executing its hybrid cryptographic locker, it modifies the Windows registry to expose hidden network drives, kills enterprise database services, and purges all local recovery vectors. Concurrently, the attackers exfiltrate gigabytes of sensitive corporate data to dark web servers, weaponizing it for a secondary extortion threat. Defeating this syndicate requires a strict understanding of how MedusaLocker configures its runtime environment and processes its encryption blocks.

1. Threat Identification & Artifact Signatures

MedusaLocker affiliates customize their payloads to evade static heuristic detection. Tracking the variant requires mapping its specific forensic footprint. The .hamster15 attack exhibits the definitive architectural signatures of a modern MedusaLocker deployment.

2. Execution Mechanics & The Registry Exploit

MedusaLocker does not blindly encrypt the local host upon execution. It is engineered to maximize its impact across an entire corporate domain. To achieve this, the binary must manipulate the host operating system’s internal configuration to expose as much data as possible.

The EnableLinkedConnections Registry Manipulation

A standard Windows security feature dictates that elevated processes (running as Administrator) do not share the same mapped network drives as standard user processes. This acts as a natural barrier to ransomware.

MedusaLocker bypasses this limitation by directly modifying the Windows registry. Upon execution, the malware injects the following configuration:

Hive: HKEY_LOCAL_MACHINE
Path: SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
Value Name: EnableLinkedConnections
Type: REG_DWORD
Data: 0x00000001

By forcing this registry value to 1, the operating system merges the network connections between filtered and elevated security tokens. Suddenly, every hidden SMB share, NAS device, and mapped departmental drive connected to the host becomes visible and accessible to the ransomware’s elevated encryption threads.

Autonomous Network Traversal

Once the registry is modified, MedusaLocker begins an aggressive reconnaissance loop. It executes an ICMP (ping) sweep across the local subnet to discover active IP addresses. It then systematically attempts to authenticate to any active Server Message Block (SMB) port (Port 445) using the compromised user’s credentials. If successful, it encrypts the remote files over the network without ever needing to drop a payload on the secondary machine.

3. The Cryptographic Architecture of MedusaLocker

The developers behind the .hamster15 variant utilize a robust hybrid cryptographic model. Understanding this math is critical for identifying potential recovery vectors.

Symmetric Block Cipher and Asymmetric Wrapping

To encrypt file data quickly, MedusaLocker generates a unique, localized symmetric key (typically utilizing AES-256 in CBC mode). Every target file is read, scrambled using this symmetric key, and overwritten on the disk.

If the malware left this symmetric key in plain text, incident responders could simply reverse the encryption. To prevent this, MedusaLocker embeds the threat actor’s master public asymmetric key (RSA-2048) within the compiled binary. The symmetric AES key is mathematically wrapped (encrypted) by this public RSA key.

This results in a highly secure, encrypted metadata block. In this specific affiliate branch, instead of only appending this block to the end of the encrypted file, the malware converts the encrypted key blob into a massive hexadecimal string and embeds it directly into the ransom note as the Key ID. Decryption requires the attackers to load this Key ID into their private server, applying their master private RSA key to unlock the underlying AES key.

4. System Demolition & Anti-Recovery Tactics

To ensure the victim is entirely dependent on the ransom payment, MedusaLocker runs a series of destructive batch commands hidden in the background immediately prior to encryption.

• Service Assassination: The malware iterates through the Windows Service Control Manager (SCM), sending terminate commands to over 50 specific services. This primarily targets Microsoft SQL Server (sqlservr.exe), Oracle instances, Microsoft Exchange, and backup agents like Veeam and Acronis. By killing these services, it releases the file locks on high-value databases, allowing the ransomware to scramble them.
• Shadow Copy Purging: It executes direct shell commands to wipe out native Windows recovery options:
  vssadmin.exe Delete Shadows /All /Quiet
bcdedit.exe /set {default} recoveryenabled No
wmic.exe shadowcopy delete

5. Verbatim Ransom Note Reference Log

Verify that your system’s dropped HTML or TXT files match this architectural layout, specifically noting the aggressive double-extortion claims and the massive Hexadecimal Key ID:

6. Enterprise Incident Containment and Response Playbook

If your security operations center detects active file manipulation or identifies the .hamster15 (or higher) file marker, execute this immediate isolation playbook to limit data damage:

1. Isolate Network Routing Boundaries: Disconnect compromised host servers from the local switch infrastructure immediately. Pull physical network lines. Because MedusaLocker aggressively scans SMB shares, severing the network connection instantly halts its ability to encrypt secondary NAS devices or file servers.
2. Execute Live Volatile Memory Capture: Do not reboot the compromised machines. A system reboot flushes the volatile RAM cache, destroying cached encryption keys and active process structures. Run an administrative memory acquisition utility (such as DumpIt or FTK Imager CLI) straight from a secure, write-blocked external storage device to save a complete image file of the host’s volatile memory.
3. Terminate Cryptographic Processes: Open Process Explorer using administrator privileges. Look for anomalous execution patterns coming from local temporary directories or unverified services. Right-click the suspicious entry and select Kill Process Tree to stop active disk writes.

7. Institutional Laboratory Reconstruction Blueprint

Overcoming a targeted MedusaLocker attack requires a strict, scientific laboratory framework that prioritizes data integrity. Automated internet recovery tools will only cause further, permanent damage to the sector structures.

• Sector-Level Drive Cloning: Before any extraction or parsing attempts begin, forensic specialists create a complete bitstream copy of the compromised media using hardware write-blockers. All analytical and repair tasks run safely on these clones.
• Unallocated Space Carving: Ransomware often operates by reading a file, encrypting it in memory, writing the new encrypted file to disk, and then deleting the original. If the system was contained quickly, deep byte-level carving can bypass the encrypted .hamster15 files entirely and extract the raw, deleted original files directly from the physical disk sectors.
• Shadow Copy Remnant Extraction: Even though MedusaLocker executes vssadmin delete shadows, large enterprise storage arrays occasionally fail to clear historical data blocks completely. Deep-sector analysis can locate and extract viable remnants of deleted shadow copy points for partial rollbacks.