crysis

[Content by Gemini 2.5]

Technical Breakdown – CrySiS / Dharma / .wallet / .onion / .java / .bip / .combo / .xxxxx family

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CrySiS does not use a single fixed extension.
    Historically you will see:
    .wallet, .onion, .java, .bip, .combo, .arrow, .brr, .write, .red, .cezar, .combo, .cobra, .ETH, .air, .van, .AUF, .AUDIT, .kyra, .Adame, .btc, .domn, .shadow, .cezar, .arrow, .muslat, .hets, .berosuce, .guvara, .coharos, .nacro, .mtogas, .londec, .nelasod, .format, .bkpx, .lalo, .hbdal, .nbes, .gesd, .righ, .merl, .kodg, .meka, .tosk, .carote, .rostic, .brusaf, .faust, .laccd, .qcmb.

    Important: CrySiS derivatives add the e-mail address and a random-ID after the extension, e.g.
    report.xlsx.id-[3B4C5E5F-2776].[[email protected]].guvara

  • Renaming Convention:

  • The original filename is kept but a triple suffix is appended:
    <original.name>.id-<8_HEX>.[<attacker_email>].<variant_extension>

  • Example: 2019_bud.xls.id-1E857D00.[[email protected]].cobra

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
  • First surge: – observed as early as September 2016 under the name CrySiS/.wallet.
  • Re-branding / active re-distribution waves in:
    • Q3-Q4 2017 (Dharma)
    • January 2019 again after private key leak (see below)
    • May–October 2020 – re-surfaced with RDP-combo campaigns during COVID-19 rush to remote work.

3. Primary Attack Vectors

  1. Remote Desktop Protocol (RDP) – brute-force or password-spray against port 3389/TCP, then manual on-keyboard tool-drop (to C:\ProgramData\oracle.exe, C:\Intel\svhost.exe, etc.).
  2. Exploit Kits – older versions occasionally used RIG / Sundown.
  3. Stolen / phishing credentials – harvested from underground forums or previous breaches.
  4. SMB & EternalBlue attempts – NOT a primary vector but seen in blended attacks.
  5. Supply-chain infection on MSP/NOC tools – threat actors purchased RDP access via “RDP-shop” marketplaces.

Remediation & Recovery Strategies

1. Prevention (First 30 minutes of hardening)

  • Patch everything, but especially:
    – Windows Remote Desktop Services (BlueKeep CVE-2019-0708, among others).
    – VPN appliances / Citrix / Pulse clients if present.
  • Expose RDP only via VPN, or better, never expose 3389/TCP to the Internet.
  • Enforce MFA & complex passwords on all remote access services.
  • Segment networks – place Terminal Servers in a separate VLAN/sub-net.
  • Disable SMBv1 (via GPO).
  • Enable Windows Firewall with outbound filter that blocks SMB (135/139/445) from servers not explicitly needing it.
  • Install EDR/NG-AV on servers and high-value workstations (Microsoft Defender for Endpoint with Ransomware Protection / “Controlled Folder Access” on Windows 10/11 is sufficient when properly tuned).
  • Standard: 3-2-1 backup rule – 3 copies, 2 media, 1 off-line, test restores weekly.

2. Removal (Step-by-step)

Prerequisite: be sure you have a known-good backup before starting. The decryptor below does not delete the malware automatically.

  1. Disconnect affected machines (un-plug LAN/Wi-Fi).
  2. Boot into Safe Mode with Networking.
  3. Remove persistence:
    – Run Autoruns → check “Logon” & “Services” tabs → remove odd entries like OracleUpdate.exe, svhost.exe, tasksche.exe, random-named “helper” service.
    – Delete scheduled tasks in Task Scheduler under root and %windir%\System32\Tasks.
  4. Manually stop any remaining ransomware processes via Task Manager → “End process”.
  5. Full scan with Microsoft Defender Offline or a reputable AV (Malwarebytes 4.x, ESET, HitmanPro.Alert).
  6. Reboot and patch/reboot cycles until the system no longer reports infections.
  7. (Optional) Once verified clean, re-image the OS if any doubt remains.

3. File Decryption & Recovery

  • Recovery Feasibility: YES – some variants can be decrypted.
    On 31 May 2017 security researchers (Cisco Talos, Kaspersky, CERT-NZ) released working decryption keys and a utility for original CrySiS/.wallet v2 and Dharma v1–v2 (before 18 May 2018).
    • Tool:
    – Kaspersky RakhniDecryptor 3.1.0+ (2023 signed build)
    – Avast Decryption Tool for Dharma/CrySiS (continuously updated).
    • How to use:
    1. Find one original file and its encrypted copy—pairs must rely only on identical file types.
    2. Copy both to a working directory.
    3. Run the tool → select the encrypted file → tick “Original copy” → proceed.
    4. Program runs offline (no network required) – decryption can take minutes to hours depending on file count.
  • For 2018+ iterations “still-unbreakable”: only option is restore from backup or negotiation. Note that the malware does NOT delete VSS shadow-copies by default, so running vssadmin list shadows on the host may reveal intact snapshots.
  • Essential Patches / Updates:
    – Windows 10/11 – cumulative LCU KB5026372 (5/2023) or higher.
    – Microsoft “BlueKeep/Remote Desktop” patches: KB4499175/KB4499180 (for Windows 7/2008 R2) extended support.
    – If running outdated 2003/XP– disable RDP entirely.
    – OpenVPN, Cisco AnyConnect, Citrix StoreFront – current LTS releases.

4. Other Critical Information

  • Unique Behavioral Traits:
    – Selective encryption: skips *.exe, *.dll in %windir%, SysWOW64, Recycle Bin, but reverses its own logic from time-to-time between builds.
    – 2-step ransom note: ReadMe.txt directly alongside encrypted files plus Info.hta launched through the Registry run-key to open automatically on login.
    – Per-machine identifier (ID-XXXX): used to link payments; e-mails used include: [email protected], [email protected], [email protected], [email protected], etc.
    – Background singing sound (first discovered variant from 2016 made a WAV file play on infection – not present newer versions).

  • Broader Impact:
    – Healthcare/hospital downtime worldwide (2019 Mayo Clinic emergency labs).
    – Crypto-mining follow-ups: on several occasions attackers chained Dharma/CrySiS with clipboard hijackers and XMRig miners to monetize the breach further.
    – Affiliate model (RaaS): the group sells direct access (“panel + builder”) to other crews, making attribution difficult.

Rapid reference card for IR teams – hang it on the SOC wall: 

CrySiS Indicators (sample hashes, exclude anonNetworking ones):
a68f3a6…a3af.exe – 2020-oct
f1e7cc…d0f.exe    – 2021-april
SpreadServer.exe (bundle)
Registry autostart: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\mshta.exe …

Stay mindful: because CrySiS keeps getting re-packaged by multiple actors, the extension list above will inevitably grow. Always cross-reference the ransom note wording and wallet address pattern before investing time in decryption – it is easy to mistake CrySiS for a wholly new strain.