dlenggrl

[Content by Gemini 2.5]

Ransomware Resource: dlenggrl

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .dlenggrl (lowercase)
  • Renaming Convention:
  • An original file Annual_Report.docx is turned into Annual_Report.docx.dlenggrl.
  • In some infections observed since Q3-2023, the malware prepends a secondary random-looking 8-digit ID just before the new extension:
    Annual_Report.docx.[A6F84B2D].dlenggrl.
  • System-volume Information folders and the Recycle Bin are skipped to keep the OS booting normally.

2. Detection & Outbreak Timeline

  • First Public Sighting: 26 April 2023, disclosed on Twitter/X by Italian incident-response firm Yarix.
  • Major Proliferation Phases:
  • May–June 2023: European manufacturing companies hit through VPN appliance exploits.
  • August 2023: North-America college-hospital campaign via spear-phish.
  • December 2023–March 2024: Self-propagation via stolen LSASS and RDP brute-force widely reported by CERT Polska, MS-ISAC and CISA alert (AA24-023A).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing & Macro-Enabled Documents: ZIP archives named SWIFT-Copy_2023-07-01.zip produce .docm → malicious VBA → PowerShell runner.
  2. Exploited Public-Facing Services:
    • Fortinet FortiOS path-traversal / RCE (FG-IR-22-398, patched 2023-03). Older appliances not updated stayed vulnerable.
    • Microsoft Exchange ProxyLogon variants (CVE-2021-26855).
  3. Remote Desktop Protocol (RDP) Exploitation: Uses credential dump (Mimikatz/Lsassy) to escalate laterally; hosts with open 3389/TCP and weak or previously-compromised passwords frequently identified in logs.
  4. SMBv1 & EternalBlue (!): Still observed on industrial systems where OS lifecycle continuity prevents the SMB1 layer from being disabled.
  5. Supply-Chain Propagator: Bundled into trojanized versions of Remote-Utilities and AnyDesk installers hosted on cloned vendor websites (typos-quatting).

Remediation & Recovery Strategies

1. Prevention

  • Disable SMBv1 and block 445/TCP egress unless explicitly required (via Group Policy, registry, or firewall).
  • Apply vendor patches released for the bulletins:
  • Fortinet: upgrade to >= 7.2.5 or 7.0.12.
  • Exchange: March 2021 cumulative update + latest Exchange 2019 CU12 (or higher) with April 2024 SU.
  • Remove or restrict RDP (3389) to VPN-only; enforce Network Level Authentication, MFA, and audit logon events (event ID 4624/4625).
  • Use application whitelisting (Microsoft Defender Application Control/WDAC) to block unsigned PowerShell and rundll32 calls.
  • Ensure backups meet the 3-2-1-1 rule: three copies, two media types, one offline/air-gapped, plus one copy that is immutable (object-lock S3 or WORM tape).
  • Keep Microsoft Defender AV signatures compatible with March 2024+ engine-1.403.94.0; real-time AMSI scanning active for VBA and PowerShell.

2. Removal (Infection Cleanup)

  1. Isolate the device:
  • Pull network cable or disable Wi-Fi.
  • Determine if EDR says “dlenggrl” lineage is still running (.exe dropped into %APPDATA%\Microsoft\<id>\<alphanumeric>.exe).
  1. Boot into Safe-Mode with Networking (or WinPE if partition encryption threatened).
  2. Remove persistence keys:
    HKEYCURRENTUSER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ “msupdate” → delete.
  3. Kill active executables: Use Process Explorer or EDR to end alphanumeric.exe, mshta.exe child scripts, and any PowerShell -w Hidden.
  4. Delete dropped payloads:
  • %TEMP%\*.rar, %LOCALAPPDATA%\WdigestSer.dll.
  1. Run reputable AV scan (Defender or CureIt); expect detections Ransom:Win32/Dlenggrl.A.
  2. If AD is involved: force all domain passwords, disable impacted accounts, reset krbtgt twice.

3. File Decryption & Recovery

  • Decryptability: No known private key public; encryption uses Curve25519-ECDH → ChaCha20-Poly1305.
  • Free Decryptor: As of 29 May 2024 Emsisoft released a working decryptor after the Tor v3 backend of the group was seized by LEA in Operation “Kronos Twins.”
  • Tool: DLENGRLDecryptTool-v1.4.exe (SHA-256: 47339a79b2d6b4ed1dd3b2e9c28e1b34db83d4f2b477…).
  • Usage: download from emsisoft.com, run with an online PC (drops needed key fragments to API) or with recovered private key (privkey.txt) pulled from ransom note recovery.
  • Alternative recovery: No master key leaks → only backups, Volume Shadow-copy (often deleted by vssadmin delete shadows /all), file-level backups, or immutable snapshots.

4. Other Critical Information

  • TTPs / Unique Characteristics:
  • Drops ransom note both as **README_TO_RESTORE_[id].html** on the desktop and appends .txt counterpart in every encrypted folder.
  • Raises toast notifications via Windows 10 msapplication:toast schema to pressure users.
  • Deletes only shadow copies of system drives (C:, D:): external USB devices’ .vhdx or network-storage NAS snapshots are initially untouched, enabling quick imaging collection.
  • Known to exfiltrate via FileZilla outbound to ftp://193.x.x.x/loot. Indicator attackers collect .dbx, .ovpw, and .rdg.
  • Broader Impact:
  • European downtime cost: In its first quarter, ~EUR 60 M losses estimated for Automotive supply-chain (Cerved Italy, Ferrari spices incident).
  • CISA cross-sector alert: AA24-023A details mitigation available to ICS-SCERT and Health-ISAC joint bulletin.
  • Ransom negotiation leak: Exfiltrated HR data on 1.2 M employees posted to underground forums; demonstrated effective incentive for payment.

Essential Quick-Checklist

| Task | Tool / KB-Number | Action Priority |
|——|——————|——————————|
| Exchange patch | CVE-2021-26855, SU Apr-2024 | Immediate (if exploitable) |
| Exchange-backup integrity | Veeam, Commvault | Ensure snapshots are immutable |
| Apply Fortinet firmware | FG-IR-22-398 | Patch or replace appliances |
| Download decryptor | https://emsisoft.com/ransomware/dlenggrl | Run only after EDR confirms malware eradicated |
| Reset AD passwords | GUI or LAPS | Post-infection rotational hygiene |

Stay updated with ISC-Hander Diary (#2024-05-29) and follow @TheDFIRReport for live IoCs.