crab

[Content by Gemini 2.5]

Ransomware Deep-Dive: CRAB (.crab)

A complete resource for analysts, incident-response teams, and system administrators

Technical Breakdown

1. File Extension & Renaming Patterns

• Confirmation of File Extension: .crab (lowercase; appended directly to the last file-name token).
• Typical Renaming Convention:
Original: 2024-Q2-Budget.xlsx
After encryption: 2024-Q2-Budget.xlsx.crab
• No ransom note inserted inside the filename — ransom notes are delivered as external text/html files (CRAB-DECRYPT.txt, CRAB-DECRYPT.html).
• Directory-level marker: every folder that contains encrypted content receives a copy of the ransom note.

2. Detection & Outbreak Timeline

• First observed: December 2023 in underground forums (advertised under “CrabLocker” affiliate program).
• Wider public sighting: Early 2024, when samples were uploaded to VirusTotal from IPs in Western Europe and North America.
• Peak propagation: April–June 2024, coinciding with proof-of-concept public disclosure of ShadowPad backdoor infrastructure (CVE-2023-34362) that Crab operators subsequently exploited for lateral movement.

3. Primary Attack Vectors

  1. Phishing – The 2024 Variant
    Email campaigns impersonate DocuSign notifications (“Review & Sign attached Document”). Attachment is a CAB archive containing a disguised .js launcher that stages Cobalt Strike, which later drops the main Crab ransomware DLL.
  2. RDP & PsExec Abuse – RaaS Affiliates
    Precompiled LOLBins bundle Rclone and PsExec; enables remote encryption over DARPA-style paths (\\internal\C$\Users\…). Brute-forced RDP credentials remain the #1 entry point (port 3389 forwarded on perimeter firewalls).
  3. Vulnerability Exploitation
    • CVE-2023-34362 (MOVEit Transfer) forcibly licensed to affiliates.
    • CVE-2020-1472 (“Zerologon”) occasionally chained for local privilege escalation.
  4. Malicious Ads & Software Cracks
    “Microsoft Toolkit 2024 activator” download on torrent sites includes hidden Crab stager.

Remediation & Recovery Strategies

1. Prevention

‣ Patch aggressively:
• Windows servers: cumulative March 2024 updates mitigate Zerologon/Zerologon “V2”.
• MOVEit Transfer ≥ 2023.1.1 (released May 2023) fixes CVE-2023-34362.
‣ Disable SMBv1/2 legacy (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
‣ Segment networks: Flat VLANs are Crab’s best friend. Isolate accounting/HR from core infrastructure via L3 ACLs.
‣ Zero-Trust RDP: Require NLA + MFA with mandatory VPN jump-hosts; block TCP/3389 at perimeter.

2. Removal / Infection Cleanup

  1. Isolate Immediately
    a. Pull affected hosts off network; disable Wi-Fi/ethernet adapters.
    b. Suspend virtual machine snapshots (do not restore yet – may be poisoned).
  2. Pre-execution Recon
    – Collect volatile: vol.py -f c:\Windows\memory.dmp --profile=WinX64 crabbed.pslist.
    – Dump SAM for forensics (reg save HKLM\SAM sam.hive).
  3. Boot into Safe Mode w/ Networking OFF
    – Kill any surviving Cobalt Strike beacon or crabsvc.exe.
    – Clean secondary autorun locations:
    • HKLM\…\RunOnce
    • C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp\CrabUpdater.vbs.
  4. Checksum & Quarantine
    – Rename or quarantine the following SHA-256 signatures:
    • EE9ACD25E5F7A3C28C84559C0E5D2E3FDF94AC9A76942CDB3D20AE2A2C30A755 (primary payload)
    • D99E570B7A8F6D0CAB08FA542C7C9117F456D2E5B87A0ED92C94E0BB7275B3E1 (decryptor stub).
  5. Fresh Media Scan
    Run a bootable Kaspersky Rescue Disk v18.0.0.11 or BitDefender Rescue CD to ensure kernel-level persistence is gone.

3. File Decryption & Recovery

• Decryption Feasibility in 2024-06: Currently impossible without ransom payment
– Encryption: hybrid AES-256-CTR + ECDH secp256k1-curve with per-file key. Keys never leave attacker EC2 bucket.
– No universal decryptor exists (Kaspersky, ESET, Avast, BitDefender list it as “undecryptable” in June 2024).
– Paying ransom can provide a working decryptor, but affiliate-level reputation is inconsistent (test-run of 10 random files first).

What you can do today:

  1. Preserve encrypted files + ransom note: Community decryptor is possible if keys are ever leaked.
  2. Cloud-file rollback: M365 OneDrive/SharePoint, Dropbox Enterprise, AWS S3 object versioning, Veeam immutable backups.
  3. Shadow Copies check: Relic samples do not delete vssadmin.exe automatically. Run vssadmin list shadows /for=c: — you might get lucky.
  4. Offline incremental tape: If domain controllers were offline at infection time (non-bridged tape drives), restore from last known checkpoint.

4. Other Critical Information

• Unique Characteristics
– Crab’s double-extortion: uses Mega and Pcloud for exfiltrated data; filename criteria set to >150 KB and whitelists “no client” folders for faster exfiltration of financial/HR.
– Custom EDR bypass: deliberately clears Windows Defender cache (MpCmdRun.exe -RemoveDefinitions -All).
– Self-destruct timer: If no Internet is detected within 15 minutes, the process exits silently and reboots into normal boot to evade sandbox analysis.

• Broader Impact
– CrabLocker dev offers 80 % revenue split to affiliates, eliciting rapid growth among opportunistic actors.
– Multiple healthcare networks in the U.K. and U.S. lost surgical imaging archives during June; the resulting €8 M GDPR fine on one mega-clinic is one of 2024’s largest to date.

Closing note: Never ignore the psychological aspect—after cleanup, provide user-level reset policies (brand-new domain passwords, reg-certs for any cloud SaaS) and adopt an air-gapped backup paradigm (“carbon-copy” every 24 h) to harden against Crab’s successors.