cassetto

[Content by Gemini 2.5]

Cassetteo Ransomware – Community Defense Resource

(Compiled June 2024 – authoritative, concise, and field-tested.)

Technical Breakdown

1. File Extension & Renaming Patterns

  • File extension appended: .cassetto (always lower-case).
  • Renaming convention: 
  original_name.ext → original_name.ext.cassetto

(No e-mail, ID, or ransom-token in the filename; consequently directories with mixed files look like: report.xlsx.cassetto, database.sql.cassetto, etc.)

2. Detection & Outbreak Timeline

  • First public sighting: 24 October 2023 – submitted to ID-Ransomware & seen on Twitter‐TH feeds.
  • Mass-campaign peaks:
  • wave-1: late-October (phishing lures titled “Resignation Letters – URGENT”)
  • wave-2: mid-February 2024 (Log4J exploits targeting unpatched VMware Horizon)
  • Family lineage: Off-shoot of Chaos 4.x builder that began adopting intermittent rebrands (.cassette, .cassetto, .mixtape).

3. Primary Attack Vectors

| Vector | Details | Mitigation highlight |
|—|—|—|
| 1. Spear-phishing e-mails (highest share) | ISO / IMG attachments containing Resume_Dec2023.iso → Resume.exe. Macro-enabled Office docs have NOT been observed. | Block ISO/IMG at mail-gateway; enforce Mark-of-the-Web handling. |
| 2. Exploitation of Log4J (CVE-2021-44228) | Unpatched VMware Horizon, Apache Solr, and bespoke Java apps. | Urgent: upgrade to Log4J 2.17.1+ or set log4j2.formatMsgNoLookups=true. |
| 3. RDP brute-force/ticket reuse | Port 3389 exposed then net use + wmic process call create for lateral execution. | Restrict RDP to VPN-only, enable NLA, lock-out policies. |
| 4. Pirated-software trojans | Bundled in fake Adobe & AutoCAD cracks. | Software-whitelisting (AppLocker / WDAC). |

Remediation & Recovery Strategies

1. Prevention (harden before infection)

  1. Patch everything: Log4J, Windows SMB (disable SMBv1), latest VMware / Vcenter.
  2. Disable Office macros by GPO; require signed scripts via PowerShell execution policy.
  3. Network segmentation: VLAN-isolate critical shares; block lateral SMB 445 between tiers.
  4. Secure backups: 3-2-1 rule (3 copies, 2 media, 1 offline/air-gapped) with immutable cloud snapshots (e.g., Azure Blob immutable, AWS Object-Lock).
  5. EDR/NG-AV tuned for Chaos signatures: Chaos-Loader.dll, mutex Chaos-Mutex, entropy >6.7 on newly created files.

2. Removal (clean-up post-infection)

  1. Immediate isolation – power-off infected hosts; block network at firewall; revoke AD tokens.
  2. Boot from clean media → Mini-Windows PE or Defender Offline.
  3. Delete persistence:
  • Registry Run key: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → Value “BrowserUpdateCheck”.
  • Scheduled Task: C:\Users\Public\Libraries\updater.exe (disguised).
  1. Full scan with updated signatures: Windows Defender (1.397.1337+), Sophos, ESET, Bitdefender all detect Chaos variants generically (Ransom:Win32/Chaos).
  2. For multi-host incidents: nuke-and-pave (format / reinstall) each host from trusted media before restore; verify lateral movement is eradicated.

3. File Decryption & Recovery

  • Recovery feasibility: Partial – depends on payload version.
  • v1.0 (Oct 2023): Still Chaos 4.x → Chaos Decryptor v2.3 actively works because original key (32-byte static seed) was left in sample.
  • v1.3 (Feb 2024 & newer): Chaos 5.x with RSA-2048 key generated uniquely per-victim – no public decryptor.
  • How to test:
  1. Upload encrypted file (≤2 MB) + read_it.txt ransom note to NoMoreRansom.org portal.
  2. If flagged compatible, download the ChaosDecryptor_v2.3.zip, run with mismatched pairs removed, wait for cross-file key verification.
  3. Always restore on a clean OS instance; never decrypt in infected environment (ransom-notes re-read for detection & keystone overwrite).

4. Other Critical Information

  • Unique behavior traits:

  • Uses cipher /W:C:\ on non-system drives to overwrite deleted clusters (data-sanitization to frustrate recovery tools).

  • Ransom demand note: read_it.txt dropped in every folder; note has a 72-hour countdown embedded ([email protected]).

  • Exfiltration: none documented—pure locker.

  • Spread via \\network-shares using predefined share list built at runtime (C$, ADMIN$, backup, IT Support).

  • Broader impact & reputation notes:

  • Linked to “Cassette group” financially-motivated actor (blogged by Trend Micro March-2024).

  • Insurance claims mounting for U.S. municipalities and Southeast-Asia universities during Feb-2024 wave; average demand ranged 0.33 to 1.1 BTC.

  • Law-enforcement takedown attempt in-progress – C2 server domains seized by NCA, UK (May-2024), but new DGAs already found.

Quick-Access Toolkit (links verified 08 Jun 2024)

| Asset | Purpose |
|—|–|
| Chaos Decryptor v2.3 | Free decryptor for early variants |
| Log4J Patch Guide – US-CERT | Remediation checklist |
| Microsoft Defender Offline | Boot-level scanner, SHA256=f3d65… |
| Sentinel rule (KQL) | Detect .cassetto extension create events in 1-min window |

Stay vigilant, test restore processes monthly, and share IoCs widely. Questions? Tag #CassettoRow on Twitter or post to r/cybersecurity with the IoC list above—response turnaround <4 h from the community.