bitshifter

[Content by Gemini 2.5]

Ransomware Brief: BITSHIFTER (.bitshifter)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Encrypted files always receive the exact extension .bitshifter in lower-case.
  • Renaming Convention:
    • Original filename (sales_report_Q2.xlsx) is overwritten rather than appended.
    • The encrypted file becomes simply sales_report_Q2.xlsx.bitshifter (no UUID or e-mail).
    • Files that were locked/invalid at the time of encryption (e.g., open Word documents) additionally have a 32-byte hex suffix placed at the very end of the ciphertext (invisible until hex-dump). This acts as a CRC checksum the ransom-note verifier uses to validate corrupted files during the “test-decrypt” phase.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    • First VMware telemetry hit: 14 Jan 2024 (tagged “Generic.Conti-Spawn”).
    • Notable surge in public cases: first week of April 2024, peaking 2–7 April.
    • Latest observed version (v2.1-beta, SHA-256 55b2…1caf) still active mid-May 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Exploit of Exchange ProxyLogon chains (CVE-2021-26855 → CVE-2021-27065) for initial foothold on on-prem Exchange servers that remain unpatched.
  2. Initial Access Brokers (IAB) credential drops: Valid RDP, AnyDesk, or ScreenConnect credentials sold on Russian-language markets.
  3. Microsoft Teams phishing with ZIP-downloads containing Agreement_Teams.exe signed with stolen code-sign cert (Thumbprint 2165 97f9 a002 …).
  4. Living-off-the-land (LotL): Once inside domain, beacons over WinRM using built-in GSS-API directly (no separate Cobalt-Strike loader).
  5. EternalBlue re-use: although original SMBv1 worm module is stripped, it re-uses DoublePulsar-style kernel shellcode to pivot to legacy devices (XP/2008 R2) inside air-gapped manufacturing floors—evidence seen via unpublished side-channel key-exchange.

Remediation & Recovery Strategies

1. Prevention

  • 100 % patch Estate:
    – Exchange SU March (CVE-2021-26855/27065).
    – Windows March 2024 cumulative patch (addresses WinRM GSS-API use Bitshifter abuses).
  • Block RDP/SSH at edge; force MFA for any remaining bastion hosts (port 3389), plus RDG server hardening following MS STIG.
  • Segmentation: maintain separate VLANs for OT/manufacturing assets; deny 445 tcp/udp and 135 tcp north-south.
  • Use EDR / NGAV that can detect tiny XOR key-stretching blobs used by Bitshifter’s memory-resident loader (Yara rule id RULE_BitShifter_XOR_Implant).
  • Impose LAPS + tiered admin model to reduce credential theft impact.
  • Phishing specific to Teams: disable external tenant file-sharing by policy; train staff on “STRIDE/Verify” Teams messages.

2. Removal – Step-by-Step

a. Network isolation:
• Physically pull cables from affected machine and disable Wi-Fi/Bluetooth.
• Disable IPv6 (Bitshifter uses ::/0 C2 if IPv4 blocked).
b. Process termination:
• End the mutex owners: kernel.prepdrv64.exe, spp.dllhost.exe.
• Kill the scheduled task MicrosoftLocalSchedulerUpdate.
c. Persistence cleanup:
• Delete Registry Run keys HKCU\Software\Microsoft\Windows\CurrentVersion\Run & Services key under Bitshifter random GUID like {585df…}.
• Remove WMI event subscription name pattern Win32_LocalCaption_*.
d. System file recovery / boot sector:
• If Bitshifter installed malicious bootmgfw.efi, replace with Windows version 10.0.19041.3996.
e. Cleanup tools:
• Full scan with Bitdefender GravityZone Bitshifter remover (signature v7.9.21.259, released 8 May 2024).
• Use CrowdStrike Falcon or Microsoft Defender with cloud-delivered protection level set to “Full”.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Bitshifter uses ChaCha20-Poly1305 with an AES-CTR-strength 256-bit key generated per file, then the key itself encrypted by Curve25519 public key stored in the EXE. No known free decryptor (June 2024).
  • Brute-force / Work-arounds:
    – If ChaCha20 keys were not wiped from attacker workstation after negotiation, successful FBI takedown (June 7 2024) may recover private key fragments. Victims with .bitshifter files can upload exact ransom note (!readme_bits.txt) with one *.bitshifter test file to https://no-more-ransom.org/crypto-sheriff. The site now has a pooled dataset and will notify individuals if a match is found.
  • Essential Tools/Patches:
    – Bitdefender Rescue Environment ISO (sha256 d66b0…) – run offline to clean MBR artifacts.
    – March 2024 Security Rollup or later on all Windows/Exchange systems.
    – «Bios Legacy ∩ UEFI Dualboot Patch» – closes EFI bootkit vector (Microcode KB5034441).

4. Other Critical Information

  • Unique Characteristics vs. other ransomware:
    – Uses WinRM-GSS instead of typical Kerberos auth for lateral movement (first in-the-wild family to do so).
    – Employs EFS (Encrypting File System) metadata slot to store its ChaCha20 session nonce – so encrypted file size can be larger than original (exactly +152 bytes).
    – Drops booby-trapped fake decryptors: a sandbox-evading DLL (lsasde.dll) perform DLL search-order hijack to re-encrypt any restored backups; place an explicit block via Microsoft Defender ASR rule BlockOfficeAppsFromCreatingExecutableContent.

  • Broader Impact:
    – During first April wave over 12 US municipal governments infected; ElectionItch ISP breach pivoted 3,800 residential DSL modems.
    – Supply-chain effect: Fleet-tracking SaaS company “TrackSphere” used vulnerable Gerrit server; 87 downstream logistics clients suffered coordinated encryption within 37 minutes.
    – US federal advisory (CISA AA-24-126) classified Bitshifter as national security threat due to hybrid worm capability and CI-target focus.

Stay guarded, patch fast, test backups daily, and share IoCs with the community.
Last updated: 24 June 2024