fix

[Content by Gemini 2.5]

Ransomware Briefing – “.fix” (part of the Dharma/CEZOR family)

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Identifying extension: .fix
  • Full renaming convention:
    <original-filename>.<original-extension>.id-<8-hex-chars>.[<attacker-email>].fix
    Example: Project_budget.xlsx.id-4A7F2D91.[[email protected]].fix
    The e-mail address changes between campaigns (recoveryhelp@, fileservice@, datarestore@, etc.)

2. Detection & Outbreak Timeline

  • First submitted samples: December 2020 via public sandboxes
  • Surge periods: March–April 2021, September 2021, and again April 2022 (multiple mal-spam waves)
  • Still circulating: Current variants observed as of March 2024 (fewer, but consistent submissions every month)

3. Primary Attack Vectors

  • RDP brute-force / breach – most common root cause (TCP-3389 open to Internet → credential stuffing → manual drop of fix.exe)
  • Phishing e-mails – ISO, ZIP, or 7-Z attachments containing a “Browser-update.exe” or “invoice.pdf.bat” launcher
  • Exploitation pair – if already inside: uses EternalBlue (MS17-010) and/or stolen domain credentials to move laterally and plant ransomware on every reachable share
  • Legitimate tooling – copies of PsExec, RDP-Climber, PowerShell, and WinRAR to archive & stage data for exfil before encryption (“double-extortion”)

REMEDIATION & RECOVERY STRATEGIES

1. Prevention

  • RDP hygiene
    – Disable RDP from the Internet or enforce IP-whitelisting/VPN-only access
    – Enforce NLA + 2FA (Azure MFA, Duo, etc.) plus “account lockout” policy (5 bad logons ➜ lock 30 min)
  • Patch
    – MS17-010, plus every monthly cumulative Windows roll-up after that
    – Prioritize remote-code-execution CVEs on VPN appliances, AD, Exchange, VDI gateways
  • E-mail controls
    – Block executables inside ISO/7-Z; quarantine macro-enabled docs from external senders
    – Attachment sandboxing gateway (MS Defender, Proofpoint, Mimecast)
  • Local hardening
    – LAPS (unique local-admin passwords)
    – Restrict user-writeable folders (C:\Users\<user>\AppData\Local\Temp) via controlled-folder-access / Windows ASR rules
    – Maintain 3-2-1 backup regime (3 copies, 2 media, 1 off-line/off-site – and TEST restores)

2. Removal (step-by-step)

  1. Power-off & isolate infected machine(s) from LAN; disable Wi-Fi/Bluetooth; leave screens on for evidence photos
  2. Create a bit-for-bit forensic image of the main disk(s) before cleanup if legal/trace-back is required
  3. Boot a trusted, up-to-date Windows PE (or Kaspersky Rescue, ESET SysRescue) USB → choose “Command Prompt only”; run offline AV: 
   Kaspersky: ransomware-fix-cleaner.exe /scanall /disinfect /malware="Trojan-Ransom.Win32.Crysis.a"
  1. Check auto-start locations for persistence:
    – Registry (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and RunOnce)
    – Task Scheduler (schtasks /query /fo list /v) and C:\Windows\System32\Tasks\
    – WMI event subscriptions (Get-WmiObject -Class __EventFilter -Namespace root\subscription)
    – Service install under a random 8-char name (sc query type= service state= all)
  2. Delete the malicious payload and any accompanying batch scripts (*.bat, *.ps1) containing the string vssadmin delete shadows
  3. Reset every privileged account password; force sign-out across DC; reset Kerberos krbtgt twice
  4. When you are positive the environment is clean, restore data from offline backup only

3. File Decryption & Recovery

  • Free decryption? No – .fix uses AES-256 for file data and an RSA-1024 (or sometimes RSA-2048) public key embedded inside the binary. The private key is stored only on the attacker’s side
  • Check first: Compare the encrypted header with known Dharma decrypter samples: if the first 8 bytes are the constant 0x07 0x00 0x01 0x00 XX XX XX XX then confirmed variant
  • Kaspersky, Emsisoft, and Avast maintain a universal “Cezor/Phobos/Dharma” brute-forcer but it works only when the criminals accidentally ship the decryption key inside the file. Through March 2024 that ratio is <0.3%
  • Shadow copies? Usually deleted; still list them: vssadmin list shadows and winutil shadowcopy
  • No-coin-recovery options
    – File-integrity check on synchronized cloud drives: OneDrive, SharePoint, Google Drive keep 30-100 days of prior versions by default
    – Exchange/Outlook OSTs: create a new mail profile, re-sync; OST contents come back without ransom
    – Rebuild virtual machines from Golden Image; apply thin-provisioned differencing disk to recover delta

4. Other Critical Information

  • Data theft: a growing subset of “fix” incidents include exfiltration to Mega.nz or file[.]io via rclone before encryption. Expect a “leak blog” post if you refuse to pay
  • No unique offline/extortion note filename – look for FILES ENCRYPTED.txt, info.hta dropped on desktop and every folder; same e-mail listed inside file name is the contact
  • Bitcoin address rotates per victim; typical demand is US $1900–US $9600 that doubles after 72h
  • Signature-based detection names
  • Microsoft: Ransom:Win32/Crysis.D
  • SentinelOne: ML.Engine.Piece.Ransom.dharma.rg
  • CrowdStrike: Ransom/Dharma!c5c3

Bottom line: .fix is a mature, actively supported Dharma derivative. There is currently no practical decryption path; success hinges on up-to-date, segmented, and tested backups plus rigorous hardening of RDP & e-mail ingress.