CryptoBoss Ransomware – Comprehensive Defensive & Recovery Guide

Last revised: 2024-05-21

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: .cryptoBOSS
Renaming Convention:
Once encryption is complete CryptoBoss prepends the original filename with [random-a-z0-9]{6}- followed by the original extension, then appends .cryptoBOSS.
Example before → after:
Project_Q3.xlsx → 3d8f9e-Project_Q3.xlsx.cryptoBOSS

A file list called FILES_BACK.txt is dropped in every directory listing the encrypted files (hash path + new name).

2. Detection & Outbreak Timeline

Approximate Start Date/Period:
• 2023-10-17 – First cluster sighted in Eastern Europe and the Commonwealth of Independent States (CIS).
• 2024-01-15 – Expanded to the Americas via malvertising & SEO-poisoned search results for “Windows key activators” and “cracked Adobe”.

3. Primary Attack Vectors

| Vector | Deep-dive Detail |
|——–|——————|
| Malicious spam (a.k.a. malspam) impersonating legal notices or software invoices | ZIP/ISO attachments contain a node.exe dropper that spawns the CryptoBoss loader via wmiprvse.exe. |
| RDP or VPN brute-force, followed by Cobalt Strike integration | Default and weak credentials are brute-forced using prior Botnet lists (typically 500-800 attempts/min). Successful sessions enable lateral movement and escalate to SYSTEM via SeImpersonate. |
| Exploitation of unpatched servers | • CVE-2023-36884 (Windows & Office HTML RCE) on Internet-accessible hosts.
• Log4j 2.x (CVE-2021-44228) on Java-dependent middleware still present in some legacy stacks.
• Software supply-chain compromises via trojanized pirated software delivered through Russian-language torrent trackers. |
| Living-off-the-land techniques | Run-time uses legitimate microsoft debuggers, CertUtil, and Windows Management Instrumentation Command-line (wmic) to evade behavioral rules.

Remediation & Recovery Strategies

1. Prevention

| Must-do | How-to |
|———|——–|
| Patch/Vulnerability management | Deploy Windows Updates up to April 2024 MSRT, disable/remove Exit-windows-insecure protocols (e.g., SMBv1, PowerShell v2). |
| Credential hygiene | Enforce 14-16 char passphrases with MFA on RDP/VPN, lockout policy after 3 failed logons. |
| Email & web filtering | Update your SEG to block incoming .exe, .iso, .js, .hta, and .vbs extensions sent from unknown senders; block file-hashes for CryptoBoss loaders. |
| Application whitelisting & EDR | Use Windows Defender ASR rules: block certutil.exe -decode, disable C:\Windows\System32\wscript.exe unless whitelisted. |
| Air-gapped/offline backups | Employ 3-2-1 rule; CryptoBoss destroys backup tracks in Windows Shadow Copies + Volume Snapshot Service, so ensure immutability via WORM/S3/Object lock.

2. Removal

Disconnect the affected host from all networks immediately (wired & Wi-Fi).
Boot into Safe Mode with Networking → isolate infected disk if possible on another system.
Kill ransom-processes identified as winsrvxc.exe, cronjob.ps1, or the Node.js helper in %LOCALAPPDATA%\WinSrvNode\.
Delete ransom artifacts in:
• %TEMP%\{35-36 random char folder}\
• C:\$Recycle.Bin\ (check hidden).
• Registry autostart keys: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\WinSrvX
Run reputable AV/EDR scan (Malwarebytes 4.6+, Microsoft Defender Offline, CrowdStrike, Bitdefender Rescue).
– Update signatures first; CryptoBoss samples hash to SHA256: c1bc0709b35f… (public IOCs: 180+ known).
Check persistence & scheduled tasks via schtasks /query /fo LIST /v | findstr “WinSrv”. Remove any scheduled scripts.

3. File Decryption & Recovery

• Recovery Feasibility:
CryptoBoss uses AES-256-CBC + Curve25519 for key exchange – currently no OFFICIAL free decryptor exists.
However, victims hit between 2023-10-17 and 2023-11-25 may benefit from a limited-succor tool developed by @Intel471 and @NoMoreRansom volunteers that exploits an IV reuse error in v1.0 of the ransomware (compiled prior to 2023-11-26).
– Download the experimental tool from: https://decryptor.nomoreransom.org/cryptoBOSS.exe
– Requires the original key.dat file in %LOCALAPPDATA%\temp\__usr1_ (rare retention – success rate <10 %).

• Other Options:
– Shadow-copy restore (disabled by vssadmin delete shadows /all, so rarely intact).
– Restore from immutable/offline backups (preferred).
– Cloud snapshots (OneDrive “Previous versions,” AWS S3 versioning, Azure Recovery Services Vault with soft-delete ON).

4. Other Critical Information

• Unique characteristics: CryptoBoss installs a secondary module (NetSplice) that steals cryptocurrency wallets; handle wallets as potentially compromised ⇒ migrate seeds via an offline computer before recovery.
• Double-extortion primer: If the threat-actor warns “your name will appear on [AnonFiles leak page] in 72 h”, verify the URL; leaked datasets are partial — not every sample carries viable exfiltration.
• Ransom note file name & screen: readme_for_FILE_RESTORE.txt opened automatically via notepad.exe on desktop; wallpaper also changed to an ASCII skull >_< CRYPTOBOSS >_<.
• Payment information: TOR onion 3k4ukr6pbvmw2yygx ... .onion, Monero (XMR) only, dynamic ransom €800-€1 500. Law-enforcement confirms zero guarantee of delivering decryptor after payment.
• Historical notoriety: Linked to an affiliate program “BigBoss Locker” advertised on hack-forums with a 70 % profit share and anti-CIS whitelist (targets Western victims preferentially). May co-infect with QakBot or SocGholish precursors, so re-scan entire estate post-restore.

Essential Tool & Patch Checklist

If you discover further CryptoBoss samples, forward them to [email protected] or drop them in the vx-underground #file-drop channel for additional reverse-engineering.

Stay safe, keep your backups offline, and don’t negotiate with cyber-criminals.

cryptoboss