drycry

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .drycry (lowercase) is appended as a secondary extension – e.g.
    Annual_Budget.xlsx.drycry, project_mng.mdb.drycry, Client_DB.sql.drycry.

  • Renaming Convention:
    Files keep their original base-name and first extension; only the final .drycry tag is added.
    No e-mail address, random ID, or ransom-token inside the filename itself.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First submissions to public malware repositories and ID-ransomware services: mid-November 2022.
    Active distribution spikes observed Nov-Dec 2022, smaller waves Q1-2023.

3. Primary Attack Vectors

| Vector | Details / Defensive Notes |
|——–|—————————|
| Phishing e-mails with ISO/IMG attachments containing a .NET loader | ISO bypasses MOTW; always block ISO/IMG at the mail-gateway if your org does not need them. |
| Remote-Desktop brute-force → manual drop | Exposed RDP (TCP/3389) is the #1 entry seen in incident-response reports; lock RDP behind VPN and enforce 2-FA / account lockout. |
| Smuggling via cracked-software sites (“KMS”, Adobe, Office activators) | Delivered as a self-extracting RAR that launches the loader; educate users, monitor for unsigned executables in %TEMP%. |
| Living-off-the-land staging with PowerShell and BitsAdmin | Uses powershell -e (encoded) to fetch next-stage binary, then bitsadmin to pull the actual encryptor; enable PowerShell CL logging & ConstrainedLanguageMode. |

Encryptor itself is a 32-bit MSVC binary (drycry.exe, compiled 2022-11-xx) that:

  1. Deletes shadow copies with vssadmin delete shadows /all;
  2. Stops SQL, Exchange, MySQL, Oracle, Veeam services;
  3. Enumerates network shares with WNetOpenEnum;
  4. UsesCurve25519 + ChaCha20; key blob encrypted with a hard-coded master public key (RSA-2048) embedded in the file.

Remediation & Recovery Strategies:

1. Prevention

  • Patch externally facing services (especially Log4j, ProxyShell, SonicWall, Fortinet SSL-VPN, and of course MS17-010 SMB).
  • Network segmentation & zero-trust: block client-to-client SMB445, use VLANs for servers, restrict RDP to jump hosts.
  • Application whitelisting / WDAC: deny unsigned binaries in %appdata%, %temp%, \programdata.
  • Enable Windows Defender “Tamper Protection” + ASR rules:
    – Block credential stealing from LSASS
    – Block process creations from Office/ISO/Email
  • Centralised & tested offline backups (3-2-1 rule).
  • E-mail controls: strip ISO/IMG, macro scanning, rewrite .exe/.js in zip.
  • MFA on EVERY remote access vector (VPN, RDP-gateway, web-mail, SaaS).
  • PowerShell Constrained Language Mode + ScriptBlock logging.

2. Removal

Step-by-step (disconnect, revive, patch, harden):

  1. Disconnect from LAN/Wi-Fi immediately – preferably pull the network cable / disable Wi-Fi in BIOS.
  2. Boot into Safe-Mode with Networking OFF (or pull the disk and attach as RO to a forensics workstation).
  3. Identify persistence:
  • Run autoruns.exe (MS Sysinternals) → look for unsigned EXE/DLL entries, scheduled-task with random GUID name (common task name “WindowsDryUpdate”).
  • Registry: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\drvup = %ProgramData%\dll\drycry.exe –nogui.
  1. Remove above keys/tasks and the file %ProgramData%\dll\drycry.exe.
  2. Clean up dropped note: README_DECRYPT_drycry.txt in every folder (plain ASCII, no exploit code).
  3. Run a full scan with an up-to-date AV/EDR (Defender, SentinelOne, CrowdStrike, etc.).
  4. Only after the console is 100% clean: reconnect for patching.

3. File Decryption & Recovery

  • Feasibility of free decryption: NO – ChaCha20 keys are randomly generated per victim and encrypted with an embedded RSA public key. No private key is present in the binary, and no free decrypter exists (as of 04-2024).
  • Do NOT trust shady “partners” promising free decryptors – they usually just re-sell the same ransom.
  • Options are therefore:
  1. Restore from offline / immutable backups;
  2. Volume-shadow copy remnants (only if attacker failed to run vssadmin, see vssadmin list shadows);
  3. File-repair (partial) for large non-compressed materials (VHDX, SQL dumps, AVI) with tools such as PhotoRec/DDrescue to carve known headers;
  4. Negotiation/payment (not recommended): threat intel shows average ask 0.07 BTC (~US 1,800) but payment does NOT guarantee a working key and supports criminal enterprise.
  • Build an IR evidence kit before wiping: copy ransom note, encryptor binary, event logs, MFT. If a decryptor is released in the future you will need at least 1 intact file-name + encrypted pair to test it.

4. Other Critical Information

  • Unique traits that differentiate Drycry from “big-brand” RaaS:
    – No data-leak site (no double-extortion) – stolen files are not posted.
    – Single BTC address hard-coded per campaign; e-mail is not used for correspondence, only a TOX ID inside the note.
    – Encryption is “partial” – only first 1 MB of each file is touched, so carving/recovery of big media is sometimes feasible.
  • Broader impact: Because it lacks privilege escalation exploits it prefers small-medium businesses with flat networks and poor RDP hygiene. MSPs providing shared RDP-hosting have seen multi-tenant compromise → cascading incidents for downstream clients.
  • Post-incident hardening: rotate every AD account that logged in during the intrusion window, reset KRBTGT twice, audit LAPS deployment, finally review backup retention: Drycry was observed trying to age-out cloud snapshots older than 14 days.

Keep offline, encrypted backups, patch the human layer (phishing training), and restrict remote services – Drycry infections drop to near-zero once these fundamentals are in place.