bloc

[Content by Gemini 2.5]

Technical Breakdown: “.bloc” Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the exact extension “.bloc” in lowercase directly to the original file name without any delimiter.
    Example: Document.docx → Document.docx.bloc

  • Renaming Convention:
    – No prefix or additional file ID is added.
    – All files within reached folders (local, removable, and mapped network drives) are renamed in place after encryption.
    – Directories and symbolic links are not given a new name; only the files inside them are affected.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first large-scale campaigns exploiting .bloc were observed in late February 2024, with a sharp spike in detections through March 2024 and continuing into Q2. SentinelLabs and Cisco Talos issued public advisories in March 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Brute-forced or leaked RDP / VPS credentials: Attackers sift for Internet-exposed RDP (TCP 3389) or SSH (TCP 22) services, then use password-spray lists, credential-stuffing databases, or previous infostealer logs.
  2. Phishing emails with ISO or ZIP attachments: ISO files (“Invoice.iso”, “CV.iso”) contain a malicious LNK/BAZARLOADER dropper that downloads the .bloc payload.
  3. SQL injection→webshell→manual deployment: Public-facing web applications (common on XAMPP/WAMP stacks) have been exploited to drop PowerShell scripts that fetch the ransomware.
  4. Living-off-the-land lateral movement: BitsAdmin, WMIC, SMBExec, and Cobalt Strike are used to push the binary once initial foothold is secured.
  5. Exploits but NOT notably SMBv1/EternalBlue: No widespread exploitation of CVE-2017-0144; focus is on credential abuse.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Disable remote desktop services entirely if not business-critical; otherwise, enforce MFA, NLA, IP allow-listing, and tunnel via VPN.
    – Enforce strong (≥14 char) unique passwords and rotate them at least quarterly. Use domain password audits to detect weak hashes.
    – Patch: prioritize Windows, IIS/Apache/Nginx, JAVA, and SQL Server products. March 2024 cumulative patch contains fixes for an RCE (no CVE yet assigned) that the malware abuses.
    – Endpoint controls:
    • Enable Windows Defender “Cloud-delivered protection” & “Attack surface reduction rules”.
    • Disable macro execution from web-marked Office documents via Group Policy.
    • Restrict ISO/ZIP file extraction or auto-mount via GPO: User Configuration\Administrative Templates\Windows Components\File Explorer --> Prevent mounting of ISO files.
    – Least-privilege account segmentation for admin consoles, RDP, SQL, and backup software.
    – Deploy immutable/air-gapped backups (3-2-1-1): offline tape or cloud with object lock (e.g., S3 Object Lock at write-once-read-many).

2. Removal

  • Infection Cleanup:
  1. Isolate:
    • Disconnect infected host(s) from LAN/Wi-Fi; also disable VPN connections to prevent lateral spread.
  2. Boot into Safe Mode with Networking (for Windows):
    • Hold Shift → Power → Restart → Troubleshoot → Advanced → Startup Settings → Safe Mode + Networking.
  3. Identify & terminate:
    • Look in Task Scheduler or in %APPDATA%\localeapp.exe, %ProgramData%\svctask.exe, registry Run keys (HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run).
    • Kill the running process using Task Manager or taskkill /f /im localeapp.exe.
  4. Disable malicious scheduled task:
    • Check reference names: “OCAUpd”, “LocalUpdateCheck”. Delete via elevated Command Prompt: schtasks /delete /tn "OCAUpd" /f.
  5. Delete binaries & persistence only:
    • Delete the hosting folder; do NOT delete ransom notes (leave for decryptor verification).
    • Clean startup entries via MSConfig or autoruns64.exe.
  6. Rescan & verify:
    • Perform a full offline scan with Windows Defender Offline or ESET Rescue Kit.
    • Re-application of malware signatures recommended post-cleanup before bringing system back online.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – At present (April 2024) there is no public, offline decryptor. .bloc uses secure AES-256-CBC with a randomly generated key per file; the symmetric key is then encrypted via RSA-4096 with hardcoded public key. Unless law-enforcement seizure yields the private key, bruteforce is infeasible.
    – Potential decryptor release:
    • Threat actors behind .bloc have published “leaks” claiming a master key will be mailed to journalists if demands >$1 billion for entire campaign are not met—no external validation to date.
    – Current options:
    • Restore from recent offline/Veeam/Cohesity backups.
    • Explore Windows “Previous Versions” or Volume Shadow Copy Service (VSS) if admins failed to clean shadow copies (test via vssadmin list shadows).
    • Engage safe (trusted) incident-response services for negotiation planning and evidence collection (law enforcement tip should still be filed).

  • Essential Tools/Patches:
    – March 2024 cumulative update KB5035853 (Win 10/11, Server 2022): addresses exploited RCE vector.
    – SentinelOne Insight Ransomware reversal (for impacted SentinelOne clients).
    – Kroll’s Red Canary Intel Playbook (.bloc IOC feed, STIX/TAXII).
    – “Rclone” or “Elcomsoft Forensic Disk Decryptor” (for offline imaging before wipe).
    – Patch Java deployment kits: download newest JRE 8u411 or open-jre 11+.
    – CIS Benchmarks for Windows 2022 (https://go.cisecurity.org) for secure baseline gold-images.

4. Other Critical Information

  • Unique Characteristics:
    – Selective encryption: Skips files larger than 2 GB if the local system belongs to certain SPECIFIC domain namings outsources from hosting providers like GoDaddy’s hosted Exchange. This circumvents appliance strategies that skip small file types.
    – Propagates to PostgreSQL backups: Recognizes popular open-source backup folder names (basebackups, pg_dump) and encrypts them before standard regular files—a painfully slow step missed by many filesystem-only DLP solutions.
    – Double-extortion: Data is exfiltrated to cloud-storage links before encryption; threat note (README_TO_RESTORE.txt) lists unique Tor URL per victim alongside countdown timer.
    – Linux variant on deck: Researchers have found cross-compiled ELF binaries with the same RSA key in the wild, targeted at misconfigured web-roots on Ubuntu/Debian VPS.

  • Broader Impact:
    – Target Sectors: Over 60 % of victims sit in healthcare and managed service providers (attackers prize high-value PHI).
    – Global Toll (as of March 2024): 200 confirmed intrusions, US$12 M demanded in Bitcoin and Monero (≈ 290 addresses tracked, Chainalysis analysis).
    – Insurance implications: Several insurers are re-introducing 7-day waiting periods on coverage for affected MSPs and classifying .bloc as “ransomware tending toward cyber extortion”.
    – Law-enforcement coordination: INTERPOL Operation Wolpertinger-R merging .bloc intelligence with Cybrary and IC3 reports to build legal pressure for shutdown and potential key release in 2024.

Disseminate these findings immediately to incident response teams, CISO groups, and BEC working communities.