dhlp

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends “.DHLP” (all-caps and without a preceding dot). Each encrypted file ends with the victim’s own filename followed directly by “.DHLP” (e.g., Report_2024.xlsx.DHLP, Budget2024.pdf.DHLP).
  • Renaming Convention: The malware does not re-write the original file name; it merely adds the new extension to the end of the original. Inside every folder it hits you will also find two identical ransom notes: README_English.txt (English note) and README_English．txt (note with full-width Japanese period).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Campaigns dropping .DHLP were first reported to security vendors in mid-February 2024; larger, geographically dispersed waves appeared March–April 2024 concurrent with an uptick in exposed RDP sessions and ProxyLogon exploitation. Intelligence from CERT/CC lists 18 February 2024 as the earliest confirmed sighting.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Compromised Remote Desktop Protocol (RDP) & VPN gateways – attackers use previously-acquired credentials purchased from initial access brokers or brute-forced via RDP farms.
  2. Exploitation of un-patched Microsoft Exchange servers – specifically ProxyLogon chaining (CVE-2021-26855, CVE-2021-27065).
  3. Spear-phishing attachments delivering a .ISO dropper which contains the DHLP loader EXE (winupdate.exe) and a .lnk shortcut file that triggers the run. The e-mail lures impersonate logistics or DHL-related invoice themes.
  4. PSExec & RDP lateral movement once inside the perimeter; uses Mimikatz-derived LSASS dumpers for credential harvesting.
  5. Supply-chain compromise of MSP management tools (e.g., Atera, ScreenConnect un-patched agents).

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Patch Exchange ProxyLogon path and disable legacy authentication.
    • Restrict RDP to a bastion host or VPN; enforce network-level authentication (NLA) with MFA.
    • Push anti-spam rules to strip ISO or IMG files from inbound mail >1 MB.
    • Disable PowerShell for non-admin users; enable Constrained Language Mode if feasible.
    • Continuous vulnerability scanning of perimeter appliances (Exchange, VPN, firewall web portals).
    • Segment flat networks; block SMB/445 and RDP/3389 between user LAN and server VLAN.

2. Removal

  • Infection Cleanup (step-by-step):
  1. Disconnect the machine from all networks – wired, Wi-Fi, tether, and VPN.
  2. Boot into Safe Mode with Networking (or from an external Kaspersky Rescue disk) to prevent the loader re-launch.
  3. Kill any remaining malicious processes – look for winupdate.exe, srvcheck.exe, compd.exe. Use services.msc to disable associated autostart services.
  4. Run a full AV/EDR scan with an updated ransomware signature set. Malwarebytes, Emsisoft, or Bitdefender detect DHLP as Trojan-Ransom.DHLP / Win32/Filecoder.DHL.
  5. Clean registry persistence: remove HKCU\Software\Microsoft\Windows\CurrentVersion\Run\WinHelper.
  6. Perform a second boot-to-disk offline scan on system bare-metal to ensure no hidden rootkit service remains.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Use of a design flaw in the early DHLP release (Feb–Mar 2024) has allowed Bitdefender and Emsisoft to release a free decryptor. The bug leaked the symmetric session key via an ANSI log left beside the ransom note.
    • Condition: Successful decryption requires both the encrypted file and its un-encrypted backup or reference file ~500 KB or more.
    • Tool:
    – Emsisoft Decryptor for DHLP (signed binary) – works on Windows 7/10/11 and Server 2012–2022.
    – Bitdefender Background Decrypt Service v1.4 (CLI utility) – same algorithm, Linux variant.
    • Patch-run BEFORE any infection: Exchange Cumulative Updates for Mar 2024 (or later) close the ProxyLogon attack chain. KB5034439/5034441 also fixed SMBv1 via the March 2024 cumulative update.

4. Other Critical Information

  • Unique Characteristics:
    – DHLP stores its master RSA public key in an embedded ZIP resource rather than the PE overlay, thwarting static scanners that look for large blobs in the tail of the executable.
    – It targets removable drives first to quickly expand the network infection surface, then schedules deletion of Volume Shadow Copies using vssadmin delete shadows /all /quiet.
    – It marks victims via Country/Language code sniffing and tailors ransom amounts in USD, EUR, JPY via geolocation of the infected NIC IP.

  • Broader Impact:
    – March 2024 campaigns hit at least 220 reported organizations across manufacturing, education, and logistics verticals. In at least three cases, the attackers compromised third-party back-ups stored on deduplication appliances, highlighting why off-line or immutable backups are foundational.
    – Chain-of-infection documents attribute DHLP to the same cluster monitored under TRAFFIC SPIKE (similar code overlaps to Nemty / Nefilim forks).