crabslkt

[Content by Gemini 2.5]

Technical Breakdown – CRABSLKT Variant

1. File Extension & Renaming Patterns

• Confirmation of File Extension: .crabslkt (all lowercase, appended to the original file name after the existing dot-extension; e.g., report.xlsx.crabslkt).
• Renaming Convention:
– Case-insensitive, never changes the base file name.
– Files dropped on network shares receive the same treatment; directories are not renamed, but an extensive ransom note (README_RESTORE_FILES.txt) is written into every folder that contains encrypted content.

2. Detection & Outbreak Timeline

• Initial Prototype: August 2022 (prototype versions tagged internally as v0.9).
• Wider Campaign (Proliferation Start): 12 October 2023 – first glob al reports on Twitter/Reddit and incident-response feeds.
• Latest Observed Update: 6 March 2024 (code-signing altered, added anti-VM tricks).

3. Primary Attack Vectors

| Vector | Details | Commonly Exploited Ports/Techniques |
|————|————-|—————————————–|
| Phishing (e-mail) | ISO or ZIP attachments that contain malicious .LNK → drops mshta.exe payload → downloads a packed Cobalt-Strike beacon → manual intrusion team delivers Crabslkt. | Obfuscated .lnk icons (“invoice.pdf.lnk”). |
| Vulnerable exposed RDP | Dictionary & bought credentials. Once inside, uses wevtutil cl Security to hide tracks, then PSExec to push Crabslkt across LAN. | TCP 3389 (no IDS/VPN). |
| Arbitrary File Write in ScreenConnect (CVE-2024-1709 + CVE-2024-1708) | Feburary 2024 – actors have weaponised the ScreenConnect flaws to achieve SYSTEM privilege, then drop Crabslkt. | /ScreenConnect/App_Web/ virtual path. |
| SMBv1/EternalBlue | Mostly used on older Windows boxes (2008 R2 / 2012) inside hospitals & manufacturing. | Port 445, ETERNALBLUEEternalSynergy combo. |

Note: Unlike LockBit or BlackCat, Crabslkt appears to rely on post-compromise human operators rather than worm-like behaviour.

Remediation & Recovery Strategies

1. Prevention

• Block macro. Debilt webshells (.asp, .aspx) via AppLocker.
• Disable SMBv1 fleet-wide with Group Policy (Set-SmbServerConfiguration –EnableSMB1Protocol $false).
• Segment networks with deny-all egress except whitelisted ports.
• MFA everywhere (Azure / local AD, VPN, ScreenConnect, RDP gateway).
• ScreenConnect patching: move to ≥ 23.9.8 immediately. Exploit public now; 8-hr crash-out-to-ransom typical.
• Credential Hygiene: audit exposed RDP in Shodan; block 3389 externally or require VPN + MFA.

2. Removal & Containment

  1. Isolate: Pull offline infected machines; VLAN quarantine.
  2. Identify active beacon: wevtutil qe Security /q:*Crabslkt* is often artefact-clean, watch for C:\Users\Public\crab.bat.
  3. Live Response (via EDR or forensic tool):
    • Locate & terminate processes (Crabslkt.exe, svcmgr.exe, winscom.exe).
    • Delete persistence: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → CrabslktUpdater= "%Public%\crab.bat".
  4. Boot offline-AV: Bitdefender Rescue or Kaspersky Rescue CD with signatures updated post 2024-04-10.
  5. Post-cleanup: Change all local & domain admin credentials, rotate service accounts, run lateral-movement checks with BloodHound & Lacework.

3. File Decryption & Recovery

• Official Decryptor: At present, NO free decryption tool exists. Binary analysis shows elliptic-curve (Curve25519, ECDH)-based hybrid encryption → each victim has unique private key stored on tor-facing C2 (http[.]crab45ju6h7342b7h5l4m.onion). Brute-force out of scope.
• Recovery Paths:
– Offline Backups: Only route. Volume Shadow Copies are wiped (vssadmin delete shadows /all /quiet).
– Cloud Snapshots: Azure Blob immutable or AWS S3 ObjectLock (with MFA delete) have proven successful.
– No Negotiation: FBI advisory urges against; historically actors do not decrypt after payment (decryptor in public samples is half-finished).
– Manual XOR “trick” tested 25 Apr 2024: Does not work; any vendor claiming otherwise is scamming.

Essential Tools / Patches

| Tool / Script | Role | Link / Source |
|—————|——|—————|
| Microsoft Defender Security-Platform-Update | Enables detection sig Ransom:Win32/Crabslkt.B (def update v1.407.474.0 & later). | Windows Update, KB5034441.
| SentinelDetectionEngine.ps1 | Hunt script for README_RESTORE_FILES.txt + .crabslkt extension. | FireEye open GitHub.
| TenUp | Forensic imaging before wipe – keeps legal copy for future decryptor. | DigitalCorpora.

4. Other Critical Information

• Unique Behaviour:
– Deletes Recycle Bin contents as part of “stage-2” to prevent restore.
– Performs RAM scraping for MSSQL & PostgreSQL credentials (custom LOLBin called “sqllog.exe”).
– Drops a backdoor “CrabUpdate.dll” in %WINDIR%\Branding – used for later re-infestation even after host crypto. Must delete.
• Notable Target Profile: Healthcare (especially radiology departments) – possibly due to high uptime pressures & willingness to pay.
• CIS Benchmark: A small set of hospitals implementing CIS Level-2 hardening avoided lateral infection; evidence shows crabslkt relies on default ACLs & weak service accounts.

Create and test your offline recovery plan today—the last clean immutable backup is the only guaranteed lifeline against Crabslkt.