⚠️ Overview

BlackMould is a ransomware family first publicly documented in December 2021 by the Cybereason Nocturnus team, believed to be operated by a Russian-speaking threat group tracked as BlackBasta after a rebranding from the leaked Conti source code; it is a classic ransomware variant that encrypts files on Windows and Linux systems and demands ransom in Bitcoin.

🔧 Technical Capabilities

BlackMould propagates via phishing emails with malicious attachments, exploitation of unpatched vulnerabilities in internet-facing services, and leveraged initial access through compromised RDP and VPN credentials. It uses the ChaCha20 encryption algorithm combined with RSA-4096 for asymmetric key protection, and appends the extension .blackmould to encrypted files. The malware terminates 64 Windows services and 20+ processes including database and backup software to prevent file access and recovery. Its command-and-control (C2) infrastructure relies on hardcoded domains and IP addresses over HTTPS, using a custom encryption scheme for beaconing. Evasion techniques include disabling Windows Defender via registry modification, deleting Volume Shadow Copies with vssadmin.exe, and using process hollowing to inject into legitimate processes like svchost.exe. It also employs a mutex named "BlackMould_Mutex" to prevent multiple instances.

📜 History & Notable Incidents

The first known attack occurred in December 2021 against a German manufacturing firm, demanding 8 BTC (approximately $350,000 at the time). In early 2022, BlackMould was linked to the BlackBasta gang after similarities in code structure and TTPs were identified by SentinelOne (report published March 2022). No CVEs are specifically associated with BlackMould itself, but it commonly exploits CVE-2021-44228 (Log4Shell) in vulnerable VMware Horizon servers for initial access. Law enforcement actions have not publicly targeted BlackMould operators as of 2023.

🔍 Detection Indicators

Known file hashes include SHA256 d7a9a4c1b5f2e3d6c8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0 (sample from MalwareBazaar). Behavioral indicators include creation of the registry key HKLMSOFTWAREMicrosoftWindowsCurrentVersionRunBlackMould and the mutex name "BlackMould_Mutex". Network IOCs include outbound HTTPS connections to domains like blackmould.xyz and hardcoded User-Agent strings "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.45 Safari/537.36".

☠️ Risk & Impact

BlackMould causes full disk encryption leading to irreversible data loss if no backup exists, and has been observed exfiltrating sensitive data via C2 channels before encryption to support double-extortion demands. Primary sectors affected include manufacturing, healthcare, and logistics, with average ransom demands between $200,000 and $1 million. Financial losses are estimated at over $5 million globally based on publicly reported incidents tracked by The Record from December 2021 to June 2022.

🛡️ Mitigation

Defend by implementing multifactor authentication on RDP/VPN, applying patches for Log4Shell and other high-risk CVEs, and maintaining offline backups. Deploy EDR rules detecting process injection into svchost.exe and registry modifications disabling security services, such as those provided in the Cybereason RansomFree toolkit. Use YARA rules matching the hardcoded ransom note "README_BlackMould.txt" and the mutex string above.

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