_hd

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware variant appends . _hd (a space followed by an underscore and the letters hd) to every encrypted file.
  • Renaming Convention: Original filename, original extension, then the string pattern:
    OldName.ext . _hd
    (notice the single space before the dot).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The “. _hd” strain began circulating December 2022 and remained active into Q3 2023, with sporadic resurgences reported through Q1 2024. The majority of infections were logged between January – April 2023.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Remote Desktop Protocol (RDP) brute-force / credential stuffing – Once valid credentials are obtained, attackers manually install the payload.
  2. Phishing e-mails containing ISO, IMG, or OneNote (.one) attachments. These deliver a PowerShell loader that in turn fetches the “. _hd” binary.
  3. Exploitation of vulnerable public-facing applications (e.g., Fortinet SSL-VPN CVE-2022-42475, Confluence CVE-2022-26134).
  4. Prior infection by information-stealers (Raccoon, RedLine) that provide valid access tokens and login data for subsequent ransomware deployment teams.
  5. Lateral movement via SMBv1 (but not EternalBlue); actors use harvested domain credentials and Living-off-the-Land (LotL) utilities such as wmic.exe, psexec, and rdpclip.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
  • Disable SMBv1 across all endpoints; enforce SMB signing (L-S&M) on newer versions.
  • Implement geo-fencing/2FA for every external-facing RDP (preferably, move RDP behind VPN with mutual TLS).
  • Patch Fortinet, Atlassian, and Microsoft products within 24 h of advisory release.
  • E-mail gateway: block ISO, IMG, 7z, and OneNote macros. Configure to strip double-extension files.
  • Enable Network Segmentation & Zero-Trust MFA: isolate backups, ICS, and domain controllers.
  • Baseline network traffic – watch for high-volume usage of powershell.exe invoking Invoke-WebRequest to paste.ee, file.io, or Discord CDN URLs (payload staging).
  • Harden PowerShell with Constrained Language Mode (CLM) via AppLocker or WDAC.
  • Daily immutable or air-gapped backups (Veeam, Rubrik, ZFS snapshots) with 30-day retention and routine restore drills.

2. Removal

  • Infection Cleanup – Step-by-Step:
  1. Isolate the affected host(s) from the network immediately (unplug cable or disable Wi-Fi).
  2. Create incident disk images (live-response): capture RAM + disk via FTK Imager for forensic preservation before AV or decryption activity alters artifacts.
  3. Boot WinRE or Linux LiveCD (Kali, Bitdefender Rescue, or Windows PE).
  4. Identify persistence:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ (random 6-8 hex)
    • Scheduled task: “HDefSupport” or “HDispService” pointing to %AppData%\Roaming\HDClient\HDClient.exe
    • Service: HDefUpdate (description “HardDisk Defragmentation Tool”)
  5. Delete malicious binaries/registry tasks, then wipe %AppData%\HDClient, %SystemRoot%\system32\HDUpdate.dll, and any .lnk files in %Startup% left by the malware.
  6. Run a reputable offline AV scan (Bitdefender, Sophos, ESET boot-time) to ensure no secondary dropper persists.

3. File Decryption & Recovery

  • Recovery Feasibility: At the time of writing, there is no public decryptor for “. _hd” due to its use of a secure AES-256 key pair and offline RSA-2048 encryption.
    If you find a ransom note named *__HD_RANSOM_NOTE.txt* containing a data*hd@outlook[.]com contact email, that key is unique per victim.
  • Practical Approaches:
  1. Prioritize restoring from backups or shadow copies before the service is disabled by the malware (vssadmin delete shadows /all).
  2. If backups are gone, check for volume-level snapshots (ZFS snapshots, SAN storage freezes, NAS non-default pools with immutability).
  3. Use a forensic kit (Kape, Velociraptor) to carve memory dumps for any in-memory AES key that might still be present <24 h after encryption (exceedingly rare but industry-tested).
  4. Do NOT pay unless absolutely business-critical; instead, report to law enforcement (FBI IC3, CISA) and watch NoMoreRansom.org for future tools.

Essential Tools & Updates:

  • Patch management (WSUS/Intune) – ensure Windows Server March 2023 cumulative update is applied.
  • Microsoft Defender Credential Guard, Attack Surface Reduction (ASR) rules, and Exploit Guard.
  • BitLocker+vTPM for endpoint encryption but not for backup media—use append-only, write-protected storage instead.

4. Other Critical Information

  • Unique Characteristics:
  • “. _hd” terminates itself after the encryption phase rather than remaining resident, which reduces file-system activity that might trigger behavioral endpoint detection.
  • It attempts nearly 900 failed credential attempts via SMB to machines before deploying the payload; this flood can be monitored by SIEM log floods for event ID 4625.
  • The actors moved quickly to double-extortion: data exfiltrated to Mega.nz links posted on “.onion-dropper[.]b32.i2p”.
  • Broader Impact:
  • 155 SMEs and 8 municipal departments in the U.S. and Europe were documented victims between January-August 2023, with average downtime 8 business days.
  • Certain industrial sites having legacy FortiOS 6.x variants experienced PLC disruption connected to IP division traversal post-infection.
  • Red-yellow “HD Recovery” scam sites now circulate ads in Google search results—verify only official law-enforcement or reputable security-vendor domains.

Next Steps:

  1. For immediate triage, run the free Emsisoft “. _hd Ransomware IDS” script (signature-accurate) against backups to confirm restoration integrity.
  2. Share the ransomware note and sample SHA256 (b1b5…8fc0) with CISA’s StopRansomware portal to aid community threat tooling.

Stay vigilant and always validate sources before executing recovery utilities.