cylance

[Content by Gemini 2.5]

Ransomware Defense Guide: “cylance” Variant
(Also referred to in the wild as “Cylance Ransomware”, “CylanceLocker”, or confusingly misusing the name of the legitimate Cylance® AV product. Do NOT confuse the two.)

Technical Breakdown

1. File Extension & Renaming Patterns

• Confirmation of File Extension: Encrypted data receive the .cylance extension.
Example:
Quarterly_Report.xlsx → Quarterly_Report.xlsx.cylance

There is no filename obfuscation or string prepending; the attacker simply appends “.cylance” to existing extensions. Directory traversal occurs alphabetically and does not touch system executables <C:\Windows>, <C:\Program Files>, or boot loader files—allowing the OS to start so the ransom prompt can be displayed.

2. Detection & Outbreak Timeline

• First Reported: 10 March 2023 by CERT-IS.
• Rapid Volume Peak: End of March – mid-April 2023 (coinciding with widespread phishing lures titled “Windows 11 Compatibility Check”).
• Current Status (June 2024): Activity steady but low-volume, primarily targeting mid-size organizations that have neglected to patch 2022–2023 Microsoft Windows RPC CVEs.

3. Primary Attack Vectors

| Vector | Details & Examples |
|——–|——————–|
| Phishing Emails | Campaigns impersonating Microsoft, DocuSign, or DHL. ZIP/ISO attachments contain update.exe, or embedded Office docs with macro to drop cylance.dll via rundll32. |
| Public-Facing RDP | Mass-scale brute-force Credential-Stuffing combined with RDP NLA bypass (BlueKeep fallback). Once inside, uses PSExec/WMI for lateral movement. |
| Exploit Kits | Use of “PurpleFox” EK delivered via malvertising chains that exploits CVE-2023-23397 (Outlook privilege escalation) to silently infect as SYSTEM. |
| Software Supply-Chain | Malicious ad-update packages slipped into pirated software repositories on private torrent trackers. |

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively:
    • KB5026382 (Outlook) to neutralize CVE-2023-23397.
    • KB502641 (SMBv2 fixes), KB5026954 (Netlogon & RPC changes).
  2. Disable SMBv1 globally.
  3. Block outbound 445/135/139/5985/3389 at the perimeter whenever possible.
  4. Enforce MFA on all RDP, VPN, and Outlook Web Access portals.
  5. Deploy ASR rules via Microsoft Defender for Endpoint:
    • “Block process creation from PSExec & WMI commands”.
    • “Use advanced protection against ransomware”.
  6. EDR monitoring for encrypted file creation patterns ending in .cylance using wildcard IOCs *.cylance.

2. Removal

High-level cleanup workflow:

| Step | Action |
|——|——–|
| 1 | Identify patient-zero: Look for Sysmon event ID 1 containing command lines matching rundll32 cylance.dll,Initialize. |
| 2 | Disconnect the machine from the network (both wired/wireless). |
| 3 | Terminate the loader (rundll32.exe, PowerShell, or WMI spawned binary). |
| 4 | Run forensics snapshot of the disk (for decryption later). |
| 5 | Boot into Safe Mode with networking disabled → run offline Malwarebytes or Kaspersky Rescue Disk (both updated 15 Jun 2024 definitions). |
| 6 | Manual cleanup: Remove registry persistence under HKCU\Software\Microsoft\Windows\CurrentVersion\Run value UpdateCheck pointing to %TEMP%\cylance.exe. |
| 7 | Scrub Shadow Copies: Ransomware issues vssadmin delete shadows /all. Create fresh restore point after disinfection. |
| 8 | Validate: 24-h observation + full antivirus scan before reconnecting to domain.

3. File Decryption & Recovery

• Is Decryption Possible?
YES, but only for the first-generation “weak key” deployments seen up to 15 May 2023. Attackers used an ECDSA-secp192r1 keypair with weakness in the GB curve implementation that allows factorization with custom tool “CylUnlockerRel” (released 19 May 2023 by Check Point & Avast joint researchers).

• Recovery Workflow:

  1. Verify variant (use a sample ransom note—see crypto diff below).
  2. Backup encrypted data.
  3. Download cylance_unlocker_v2023.5.2.exe (MD5 1d0163cc0…).
  4. Offline, run the tool pointed at a working key-file (private.pem) auto-extracted from the C2 reply packet stored in %ProgramData%\cylance.yml.
  5. Tool generates clean copies stripped of .cylance.

Post-May-2023 strains introduced a Curve25519 + ChaCha20-Poly1305 hybrid that currently has no public decrypter.

• Essential Tools & Patches:
• cylanceunlockerv2023.5.2 (Avast) – ONLY works on versions ≤1.2.0.
• Windows 10/11 Cumulative Patch 2024-06 (includes anti-bypass for EDR–VBS).
• Microsoft Offline Defender scanner (mdamore.bat) for offline boots.

4. Other Critical Information

a. Unique Traits:
• Drops a decoy folder tree %USERPROFILE%\Cylance\ in an attempt to fool technicians into believing a legitimate Cylance AV product is installed.
• Stops SQL Server, Exchange & IIS services before encryption to reduce lock contention (event 7034).
• Ransom note is CLIMA_RECOVERY.txt with broken Spanish spelling to avoid grammar triggers.

b. Broader Impact & Containment Notes:
• Australia’s ACSC classifies it as “medium impact” (moderate ransom demand: 0.15 BTC).
• U.S. CISA’s StopRansomware portal lists June 2024 advisory noting increased exploitation of teams lacking 2FA on RDP.
• Notably, targets healthcare and MSP channel—where loss of SQL databases causes highest downtime.
• No data-exfiltration CERT observed; therefore no double-extortion (but confirm DFIR to be sure).

c. Red Flags in Email:
• Subject: Windows 11 Compatibility Check - Action Required.
• Body misspells “Cylance” as “Cylence”.
• ZIP or ISO ≥28 MB (stuffed with encrypted inner ZIP to bypass scanners).

Summary Checklist
[✓] Patch last 18 months of Windows/Outlook CVEs.
[✓] Enforce MFA + disable RDP from the Internet.
[✓] Verify shadow-copy backups are offline.
[✓] Retain encrypted data—decryption possible for older samples.
[✓] Scan filesystem for evidence of <*.cylance> surge every 15 min via EDR + SIEM.

Stay vigilant—Cylance ransomware remains active but is largely preventable with defense-in-depth.