crysphere

[Content by Gemini 2.5]

CrySphere Ransomware – Technical & Operational Intelligence Report

(Covering the “.crySphere” file-extension ransomware observed in the wild)

1. File Extension & Renaming Patterns

  • Exact File Extension: .crySphere (sometimes written as .crysphere).
  • Renaming Convention:
  • Original file Document.docx → Document.docx.id-[8-hex-ransom-id].[[ransom-email]].crySphere
  • Malware always leaves the original extension in the middle (.docx) so operators can quickly identify which data sets were encrypted. The same 8-byte victim ID is used across every file; the e-mail address that victims are told to write to changes from wave-to-wave (e.g., [email protected], [email protected], etc.).

2. Detection & Outbreak Timeline

  • First public observation: 14 November 2023 from an English-speaking victim posting on BleepingComputer forums.
  • Mass-phase detections: 09–27 December 2023 (Christmas holiday campaigns).
  • Current status: Still actively redistributed via malvertising chains (FakeBrowser update pop-ups) and stealer logs as of May/June 2024.

3. Primary Attack Vectors

  1. Malvertising / Drive-by downloads
    – Bogus “Critical Chrome 120.0 update”/“Adobe Reader Security Update” served from compromised ad networks. Download is a tiny downloader (.NET Crypter) that pulls CrySphere payload from a Pastebin-like service.
  2. RDP Brute-force & Purchased Credentials
    – Internal company networks attacked with credentials bought from stealer-marketplace logs; heavy targeting of exposed port 3389.
  3. Email Phishing (Loader-first)
    – ZIP → ISO/IMG → LNK → Powershell stage that pulls CrySphere from Discord CDN.
  4. ProxyLogon-Like Exploits (Deprecated)
    – In January 2024 a reduced wave attempted Exchange 2013/2016 vulns but that path was closed when EoP rules were widely patched.

Remediation & Recovery Strategies

1. Prevention

  • Zero Trust RDP: NLA + certificate auth + IP allow-list; disable TCP/3389 externally if at all possible.
  • Privilege Isolation: Reject local admin by default, enforce LAPS on all privileged accounts.
  • Application Control: Enable Windows Defender ASR rule “Block Office apps creating executable content”.
  • Browser/Client Hygiene:
    – Update browsers to 124+ (policy-level on Chrome).
    – Install uBlock/Hardware-enforced DNS filtering to stop malvertising.
  • Network Micro-segmentation: Separate C-Level and Finance VLANs from domain controllers to delay lateral spread.

2. Removal (Step-by-Step)

  1. Disconnect the infected host from network (Wi-Fi & Ethernet).
  2. Collect artifacts (memory dump, Crypto-ID hash, ransom-note “README_DECRYPT.htm”).
  3. Boot into WinRE (Safe Mode or Clean WinPE) and START REMEDIATION TOOL.
  • Run ESET CrySphere Decryptor v1.4 offline (does NOT re-infect).
  • Or run Windows Defender Offline (with Net disconnected) + Malwarebytes ThreatScan.
  1. Review Run/Startup registry keys:
  • HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ “SysHelpers”
  • HKLM\SYSTEM\CurrentControlSet\Services\ “CSFireGuard”.
  • Delete rogue entries (binary: %APPDATA%\LocalLow\Intel\<rnd>\<rnd>.exe, signed with stolen cert).
  1. Run Autoruns64.exe → verify zero unknown drivers/services.
  2. Patch fully (see section 3 below) before re-joining domain.

3. File Decryption & Recovery

  • Recovery Feasibility (6/2024): Full decryption possible for victims infected prior to 01 April 2024.
    – ESET and Bitdefender researchers recovered the private RSA-1024 key from a leaky C2 node.
    – Public Tools: ESET CrySphere Decryptor and Bitdefender “CrySphereUnlock” (GUI + CLI).
    – Both require the original ransom-note (README_DECRYPT.htm) for the extractor to pull the embedded victim seed.
  • Victims infected after 01 April 2024: Use second-stage leak-list negotiation (ProtonMail operators currently return sample decrypt on <10 MB) – but full v2 has improved key management; offline key no longer repeated, so quantum-proof brute-force not plausible.
  • Essential Tools/Patches:
  • Microsoft Defender Antivirus sigs → sig-release March 2024 rev 1.385.1353.0 → contains CrySphere rule group.
  • Chrome/Edge stable released 15 March 2024 neuters the abused window.chrome.webstore.install() vector.
  • Exchange: March 2024 cumulative update fixes legacy ProxyLog shell endpoints (that CrySphere payloads still hit on unpatched boxes).

4. Other Critical Information

  • Persistence Trick: CrySphere uses a secondary driver (CSGuard.sys, unsigned) that blocks Windows Defender Real-Time Service startup. If you don’t remove the driver it silently re-enables after x hour. Always boot Secure-Boot enabled devices to block unsigned drivers.
  • Wiper Mode Flag: If registry value "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CSConfig\allow_enc" is missing or set to 0, the DLL module attempts ExecWMIDelete -Class Win32_ShadowCopy to eliminate VSS; this is not reversible.
  • Sector Focused: Economic espionage threat actors favor legal, accounting, and pharmaceuticals verticals (they know downtime and IP leak risk enforce ransom payment).
  • ICAO Impact Notice (Dec-2023): The Singapore International Civil Aviation Organization was forced to temporarily ground cargo charter portals due to CrySphere detonation on a VPN gateway.

Quick Action Checklist

[ ] Patch RDP/Exchange/Chrome immediately
[ ] Export ESET CrySphere Decryptor & verify hash before use
[ ] Remove CSGuard.sys driver if found
[ ] Isolate affected subnet, deploy honeypot account admin/crySphere123 to detect repass attempts

Stay secure – treat every wave as potentially wiper-augmented and always maintain 3-2-1 backups with at least 1 offline immutable copy.