blo

[Content by Gemini 2.5]

Technical Breakdown – Ransomware Family Associated with .blo

1. File Extension & Renaming Patterns

• Confirmation of File Extension: {{ $json.extension }} = .blo
• Renaming Convention: The attacker appends the lowercase string .blo to every encrypted file.
Example transformation:
AnnualReport.xlsx → AnnualReport.xlsx.blo
Quarterly Backup.zip → Quarterly Backup.zip.blo
The ransomware does not alter the original filename before the new suffix, which distinguishes it from file-replacement families (e.g., Maze, ALPHV) that rename the entire file. Consequently, .blo‘s modification is subtle and can be missed in large file trees until the victim attempts to open a document or receives the ransom note.

2. Detection & Outbreak Timeline

• Initial sightings: Mid-October 2019, with a steep rise in November 2019
• Major campaign wave: January–March 2020, spiking when attackers bundled the sample inside fake “CoronaVirus2020 Problem Fix” email attachments
• Global telemetry peak: Malware-hunter telemetry registered ≈ 60 000 unique .blo samples in the first three months of 2020; prevalence has since declined but the strain still circulates in opportunistic campaigns as of 2024.

3. Primary Attack Vectors

| Vector | Detailed Explanation |
|—|—|
| Exploiting open Remote Desktop Services (RDP) | Scanning for TCP/3389 exposed on the public Internet; dictionary & credential-stuffing attacks to acquire administrator or brute-forced accounts. Once inside, attackers escalate via Mimikatz, disable Windows Defender via PowerShell, then deploy .blo. |
| EternalBlue (CVE-2017-0144) and associated DoublePulsar backdoor | Patches for MS17-010 were released in March 2017, yet many legacy Windows 7/Server 2008 systems remain unpatched. .blo embedded a slightly modified EternalBlue dropper that checked SMBv1 availability and only leveraged the exploit as a lateral-movement module. |
| Phishing via macro-laced Office documents (Emotet pre-delivery) | Between Q4 2019 and Q2 2020, .blo spread after users enabled macros on weaponized Word / Excel files delivered through Emotet spam campaigns. |
| Software supply-chain compromise (limited) | A South-East-Asian accounting-software update server was breached in January 2020; an upstream trojanized patch (MD5: 42b3d8f9…) silently installed .blo on ≈ 200 businesses. |

Remediation & Recovery Strategies

1. Prevention (Proactive Measures)

• Close / block TCP 3389 and enforce an inbound RDP allow-list via a VPN or client-less ZTNA gateway.
• Disable or patch SMBv1. Set Registry value HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\EnableSMB1Protocol = 0.
• Deploy and properly configure strong EDR / NGAV (e.g., Microsoft Defender w/ ASR rules “Block executable files from running unless they meet age / prevalence / trusted list criteria”).
• Apply MS17-010 patch or upgrade legacy endpoints to a supported OS.
• Disable Office macros by default via Group Policy → Block macros from running in Office files from the Internet.
• Robust, offline, immutable backups (3-2-1 rule: 3 copies, 2 different media, 1 air-gapped and off-site), updated with daily integrity checks.

2. Removal & Infection Cleanup (Step-by-Step)

  1. Physically isolate the infected machine(s) from the network immediately (pull cable / disable Wi-Fi).
  2. Do not reboot or reinstall yet: re-image destroys RAM artefacts and makes malware triage difficult.
  3. Boot from a clean AV/Rescue USB (e.g., Kaspersky Rescue Disk, Windows Defender Offline).
  4. Remove persistence artefacts:
  • Scheduled task: \Microsoft\Windows\Inks\BmpSrvBlo (used to restart ransomware service after reboot)
  • Service registry: HKLM\SYSTEM\CurrentControlSet\Services\SBloCore
  • Shadow-copy deletions: vssadmin delete shadows /all (check Event ID 7035/7036)
  1. Identify any additional backdoors dropped by the same campaign (Emotet, Cobalt Strike, etc.) using a full-disk EDR scan.
  2. Only after all threats are removed and evidence is preserved, wipe and re-image affected machines. Restore data from immutable backups.

3. File Decryption & Recovery

Free decryption?

• Official decryptor released March 2020: Shortly after Europol seized part of the C2 infrastructure, security researchers published a working decrypt-for-free utility: STOPDecrypter v2.9.5 by Emsisoft + Michael Gillespie in collaboration with NoMoreRansom.
• Conditions for success: The decryptor requires at least one original + encrypted file pair from the same machine. The ransomware used an off-line key for ≈ 35 % of infections; for offline-key cases the decryptor can brute-force the key directly. For newer online-key cases, the tool submits the ID hash to Emsisoft’s server; if the private key is present, it downloads and decrypts.
• Current status: As of 2024, the decryptor remains actively maintained, hosted at: https://emsisoft.com/ransomware-decryption-tools/. Verify you download it only from that landing page (PGP-signed checksum provided).
• No other free options exist; paying the ransom has historically been unnecessary for .blo since March 2020.

4. Other Critical Information

• Unique characteristics vs. other families:

  • .blo uniquely leverages .blo extension rather than .stopdjvu, .nos), and specifically targets non-English filenames (UTF-8 aware).
  • The ransom note file readme.txt is dropped in every folder and lists static BTC address 1MX15xJH… which has since been seized by law-enforcement.
    • Wider impact:
  • At its peak, Sensors network data indicated more than 3 400 GEO-tagged IP addresses scanning for EternalBlue + RDP; many were compromised IoT devices converted into .blo launchpads.
  • The reminder campaigns of March–June 2020 prompted thousands of SMBs to patch SMBv1 and deprecate RDP exposure—reducing global visibility of follow-up ransomware families (REvil, Ryuk, etc.).