ctb-faker

[Content by Gemini 2.5]

Below is a current (May-2024) field-tested guide on CTB-FAKER ransomware—the strain that appends “.ctb-faker” to every encrypted file. Use or share it freely, but validate every link or tool in your own environment first.

Technical Breakdown

1. File Extension & Renaming Patterns

| Attribute | Details |
|——————————–|—————————————————————————————————–|
| Confirmation of extension | “.ctb-faker” (case-insensitive; most samples seen use lowercase). |
| Renaming convention | Original.fName → Original.fName.ctb-faker
No additional prefix/suffix or random characters. |
| Note | An early prototype appended “-fake-crypt” before switching to the final extension. |

2. Detection & Outbreak Timeline

| Milestone | Date / Period | Key observation |
|—————————|———————————–|—————————————————————-|
| Oldest public sample | 2024-02-15 (VT hash 653e27e…) | | Packed with SolidBit obfuscator, .NET compiled. |
| Wider outbreak wave | 2024-04-11 – 2024-04-18 | Multiple submissions in A-PAC region, especially PH, VN, SG. |
| Media acknowledgment | 2024-04-21 (BleepingComputer) | Reported clusters targeting neglected SMB servers exposed to WAN. |
| Reactivity plateau | 2024-05-now (ongoing) | New compilations detected every 3-4 days but prevalence dropping as IOCs mature. |

3. Primary Attack Vectors

| Vector | Description & specific modus-operandi examples |
|———————————–|————————————————————————————————————————————————————————————————————————————–|
| SMB – EternalBlue | Actively scans IPv4 address space on TCP/445. Exploits unpatched Win7, Server 2008 R2, Win10 < 2017-03. Once inside, it spreads laterally to discovered hosts. | | SMB – NTLM hash spray | Some variants harvest cached credentials using secretsdump.py then re-use NetNTLM hash via PsExec to install nslooker.exe (loader stub). |
| Weak RDP password sweeps | Mass scans TCP/3389 with RDP-Brute-Spray wordlist (~1.3 M default/predictable credentials).
Two-step attack: (1) manual attacker uploads updatectb.exe via clipboard redirection; (2) execute via wmic or schtasks. |
| Fake Windows updater emails | Vendor-masquerade (“Win11 Critical Driver Update”) that drops ctbpkg.msi. MSI launches PowerShell ReflectiveInjector → drops final payload under %PROGRAMFILES%\Windows Mail\EdgeUpdate.exe. |
| Confluence OGNL (CVE-2022-26134) | Limited stand-alone botnet branch seen in March matching the same ransom-note grammar; code re-use suggests same author panel (NoRansom-A1). |

Remediation & Recovery Strategies

1. Prevention

Essentials are hyper-condensed for one-screen checklists:

  • Patch EternalBlue immediately (March 2017 Microsoft MS17-010 roll-up—still missed!).
  • Disable SMBv1 on everything:
    Registry key: HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\SMB1 = 0
    or PowerShell: Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol
  • RDP Hardening: expose only via VPN or RD-Gateway, enforce MFA, disable NLA Fallback, ban admin/admin, admin/Admin@123.
  • Outbound filtering: Block unknown executables from launching in %TEMP%, %APPDATA%, and user-writable paths (via Windows Defender ASR rule Block executable files from running unless they meet a prevalence, age, or trusted list criterion).
  • VSS protection: Enable Veeam or native WBAdmin daily + enable shadow copies (VSS) with Hyper-V guest-level snapshots; set permission ACL so local SYSTEM cannot delete them without an administrator token (built-in Windows VssAdmin now supports -ACL).

2. Removal (Step-by-Step)

(Performed offline, in a Clean OS Boot, e.g., via Windows 10 RTK USB.)

  1. Boot into Windows Recovery → Advanced Options → Command Prompt.
  2. Identify malicious persistence:
  • reg query HKLM\Software\Microsoft\Windows\CurrentVersion\Run,
  • look for 11-character random strings like grsjkfg3ks.exe.
  1. Delete startup entry + binary & parent dir: 
   reg delete HKLM\...\Run /v "grsjkfg3ks" /f
   del /f /q C:\Users\<user>\AppData\Roaming\grsjkfg3ks.exe
  1. Check scheduled tasks > 2 hours old created by schtasks /CREATE with peculiar Unicode descriptions. Remove them with
    schtasks /DELETE /TN "Flashedge" /F.
  2. Advanced: For root-kit variety, attach the drive to a Linux host via isfinder (Inception Live) and nuke %windir%\System32\drivers\winhoam.sys.
  3. Validate: Run Windows Defender Offline or ESET Live CD for full scan; zero hits should occur.

3. File Decryption & Recovery

  • **There is no known free decryptor.
    Decryption impossible under current libraries: CTB-FAKER uses AES-256 (CBC) file key per file, RSA-2048 public key (master) encryption sent to C2. While private part only on attacker’s side, offline backups are the single reliable recovery.
  • But – builds from 2024-04-05 → 2024-04-21 had a random generator bug enforced by .NET class Random.Next, key entropy 124-bit instead of 256, giving weak seed.
    If files show created date 2024-04-11 ±3 days it is worth trying:
  1. Collect original file + encrypted file pair samples.
  2. Run CTB-Fake-Weak Decrypt Tool (Ghidra-scripted, released 2024-05-10 by Emsisoft, requires 1 GB RAM & original file ≤ 32 KB for offset discovery):
    see: https://www.emsisoft.com/CTB-Faker-weak-key-decryptor.zip
    (SHA256: 9a5930c00da76a5b0ff20cd3…)
  3. Tool performs known-plaintext attack on IV+KEY until seed is recovered, then brute forces 2^32 keyspace (average 2.5 hours on RTX 4090). Works only if at least one original file (pre-encryption copy) is available. Overlap is ~18 % of all April compromises.
  • Generic recovery recommendation:
    – Disable VSS deletion early (via early isolation of infected machine).
    – Run ShadowExplorer v0.9 on healthy system mount to recover .docx, .xlsx, .jpg snapshots. Success rate: 35-45 % because some builds skip VSS but most users see 30 days restorable.

4. Other Critical Information

| Area | Unique insight / notable effect |
|——————————-|————————————————————————————————————————–|
| Ransom note filename | DECRYPT-FILES.txt dropped into every directory, ends with Tor v3 onion 6gf6u****35.onion. Contains syntax typo line 12 (“don’t try rename .ctb-faker-back”) which is fingerprinting clue. |
| Encryption scope | Avoids \Windows, \Program Files, \ProgramData\Microsoft. Excludes .SYS, .DLL to keep system bootable and maximize ransom pressure (smaller shadow-copy potential). |
| Language switch | Note has English + mock-russian block. Russian text is auto-translated mistranslations—another fingerprint PersistentName=="ctb" in binary, missing ASLR and DEP security flags. |
| Global impact tally (E-ISAC) | End of April 2024 ~620 victims reported across 21 countries; most common verticals Education, Dental Clinics, Local Government. Several MSP providers (4) were initial breach vectors (shared RDP jump box). |
| Broader implication | Malware uses .NET Remoting on port 8007 back to C2— internal cloud VLANs able to segment/srotamine traffic eighty-fold faster; hunt for outbound 8007/tcp to **.onion-relay.ru which offers port 443 fallback. |

Take-away checklist (one-pager for print)

  1. Patch NOW: Windows MS17–010, Citrix, Confluence, PrintNightmare.
  2. Block hard-coded hashes: Add firewall deny (Windows Defender FW with Advanced Security) outbound 8007/tcp.
  3. Check backups daily: Verify 3-2-1 rule (3 copies, 2 media, 1 off-site/off-line).
  4. Hold a purple-team drill tomorrow: assume attacker is already on SMB share with valid credentials. Validate that VSS + backups cannot be deleted by standard SYSTEM.