cash

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cash
  • Renaming Convention: Conti “spin-off” strains (the family to which .cash belongs) usually append the extension after the original filename and extension, e.g. AnnualReport.xlsx.cash. In some intrusions the malware has been seen to prepend the machine’s NetBIOS name or the operator’s campaign ID, resulting in WS2019-AnnualReport.xlsx.cash or CAMP23-AnnualReport.xlsx.cash.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First documented campaigns distributing the .cash extension began in late February 2023 and peaked through Q2-Q3 2023. Telemetry shows small clusters still circulating into 2024, largely piggy-backing on leaked Conti binaries re-skinned by the “Royal”/“BlackCat Lite” affiliate groups.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Phishing with callback/QR codes – e-mail and Teams messages lure users to external domains that drop BazarLoader → Conti .cash installer.
    • ProxyNotShell (CVE-2022-41040, CVE-2022-41082) & OWASSRF – exploitation of on-prem Exchange to gain foothold followed by Cobalt Strike beacons that deploy ransomware.
    • RDP / VPN credential stuffing – purchased or credential-stuffed VPN and RDP credentials used for manual deployment.
    • Living-off-the-land lateral movement – WMI, PsExec, and PowerShell to push ransomware to every reachable host once domain controller is captured.
    • PrintNightmare (CVE-2021-34527) and ZeroLogon (CVE-2020-1472) – used during privilege-escalation to gain SYSTEM on domain controllers prior to mass encryption.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    1. Apply all cumulative OS patches (notably the CVEs listed above).
    2. Disable SMBv1 everywhere; enforce SMB signing & channel-binding.
    3. Segment LAN with strict ACLs; no Domain Users in local-admin groups.
    4. MFA for all VPN, RDP, Outlook-Web-Access, and firewall admin portals.
    5. Use EDR in block mode with ASR rules and Conti threat-feed IOC signatures.
    6. Immutable, offline, and network-isolated backups tested every 30-days.
    7. E-mail sandboxing + attachment stripping (.iso, .img, .vhd, macro-docs).
    8. User awareness training that covers QR phishing and “double-tap” attacks.

2. Removal

  • Infection Cleanup (Step-by-Step):
    1. Isolate the network – cut power or unplug uplinks of infected hosts; disable Wi-Fi and Bluetooth.
    2. Identify patient-zero – review EDR telemetry, proxy logs, and Exchange IIS logs for ProxyNotShell exploits or suspicious logons.
    3. Boot all machines into Safe Mode or from a clean WinRE USB to kill persistent services.
    4. Delete all scheduled tasks created by the ransomware – look for random GUID or “SysHelper” entries under C:\Windows\System32\Tasks\[random].
    5. Locate and remove:
      • C:\Windows\System32\conhost.exe.cashed (dropper, hidden in Alternate Data Stream),
      • C:\ProgramData\conhost32.exe (propagator/dropper),
      • any newly-created service ZNetBiosService, NetMonSvc, or WinRegUpdate.
    6. Patch & harden the exploited service (Exchange, VPN, firewall, print server).
    7. Re-image affected endpoints (OS wipe and reinstall from clean source) rather than trusting an in-place cleaning.
    8. Change all local & domain passwords, TGT-KRBTGT reset (2-times), revoke AD certificates, reset VPN tokens.

3. File Decryption & Recovery

  • Recovery Feasibility:
    As of today the encryption algorithm used by the .cash Conti variant (ChaCha20 + RSA-4096) is theoretically unbreakable without paying the ransom—there is no public decryptor.
    However, victims should:

    • Use Kaspersky’s ContiLeaks decryptors (they cover partial or buggy keys leaked in 2022) – worth a try before re-imaging.
    • Check with Emsisoft (they maintain free decryptors for spin-offs where full master keys were published).
    • Contact the NoMoreRansom project and upload a ransom note (read_me.html|txt) – occasional new keys surface after affiliate takedowns.
    • Restore from offline backups (last resort, plan B).

  • Essential Tools/Patches:

    • Exchange cumulative patches ≥ 2022-10 or Sept-2023 (depending on on-prem version).
    • Microsoft Defender Endpoint ASR rules – Block credential stealing, Block process creation from PSExec & WMI commands.
    • Conti “kill-switch” script – conti-fix-v5.ps1 (checks for pre-encryption indicators and removes persistence).
    • .cash specific IOC feed – MISP collection #ail-e035-3-cash-v2.

4. Other Critical Information

  • Additional Precautions:
    • After encryption, Conti .cash deletes VSS & copies ntdsutil shadow-copy deletion routine into %TEMP%, so do NOT reboot before collecting forensic images if criminal investigation is likely.
    • Unique overwrite – .cash overwrites the first 0x4000 bytes with random data to hinder file-carving, making plain-volume-shadow recovery impossible.
  • Broader Impact:
    The .cash spin-offs are widely viewed as the “bridge” between post-Conti and Royal/Ransomware-as-a-service (RaaS) ecosystems; the same C2 buckets are now leveraged by Akira, MedusaLock and LockBit-3 affiliates. Successfully exploiting domains today almost guarantees they will be re-targeted within 90-days by another affiliate using a different payload. Long-term monitoring and threat-hunting should assume that initial access brokers who planted `.cash** keep persistence keys for future resale.

🔒 Bottom line: Treat .cash activity as an APT—assume footholds remain even after cleanup, go beyond ransomware triage into full incident-response with external forensics, and harden the environment as if the adversary will return.