blacksun

[Content by Gemini 2.5]

Technical Breakdown: BlackSun Ransomware ({{ $json.extension }})

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    “.blacksun” – Every encrypted file on the host receives this single, fixed extension appended after the original extension (e.g., Contract.docx.blacksun).

  • Renaming Convention:

  • Name case is always lower-case and without additional dots or UUIDs.

  • Folder-level marker file BlackSun_README.txt (or .hta) is dropped into every directory containing encrypted data.

  • Volume shadow copies and most backup catalogues are renamed to match the same pattern, making roll-back detection very difficult.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First public sightings: mid-June 2023 (initially floated on underground Russian-language forums under the tagline “универсальный криптор”).
    Initial surge in the wild: July 2023 after a partner-program rebranding under the name “BlackSun”.
    Changelog posts indicate active, incremental versions released through at least Q1 2024.

3. Primary Attack Vectors

| Vector | How it is weaponized | Notable exploits observed in-the-wild |
|——–|———————-|—————————————|
| Remote Desktop Protocol (RDP) | Brute-force + credential stuffing → lateral movement across domain controllers | Incidents where BlueKeep (CVE-2019-0708) is used for initial foothold on unpatched legacy Windows hosts |
| Phishing Emails with Malicious LNK | ZIP archive impersonating “Locked Down” finance PDF uses double-extension .pdf.lnk → cmd.exe → PowerShell downloader | Campaigns (Aug 2023) leveraged OneDrive CDN links; MalDoc macros removed to evade AV sandbox |
| Exploited Public-Facing Apps | Confluence OGNL injection (CVE-2022-26134) to drop staged BlackSun PE | Once foothold gained, EternalBlue (MS17-010) re-enabled and used for worm-like propagation inside LAN |
| Malicious Updates / Third-Party Compromise | Supply-chain compromise of niche CAD add-ins; victims include >5 European architectural firms | Signed-but-repacked MSI silently installs BlackSun alongside legitimate update |

Remediation & Recovery Strategies

1. Prevention

• Patch aggressively – prioritise MS17-010, CVE-2019-0708, CVE-2022-26134, and any RDP-related flaws (KB5022282).
• Disable SMBv1 across entire estate; isolate legacy devices that cannot comply.
• Enforce MFA on all remote access (VPN, RDP, ADFS).
• Email filtering to quarantine ZIP,LNK,PS1,JSE files unless cleared by group exception list.
• Network segmentation – block lateral SMB/445 traffic between subnets that do not require file sharing.
• Threat Hunting queries – SOC should actively look for cmd.exe /c powershell -enc followed by domain-user privilege escalation.

2. Removal (Step-by-Step)

  1. Disconnect the infected machine from the network immediately (pull cable or disable Wi-Fi).
  2. Boot into Safe Mode with Networking OFF.
  3. Launch Kaspersky Rescue Disk (or offline AV) to remove the primary BlackSun payload:
  • SHA-256 blacklist: 1fef2caa6f90c66f7e6f78b7d1c9439e867c9c0f62e142e3acf … (exact hashes rotate; run VT cluster at run-time).
  1. Delete ShadowCopy bypass scripts – remove scheduled task \Microsoft\Windows\Setup\BlackSun_SVC if present.
  2. Clean up PowerShell profiles and registry Run keys that may contain stage-2 downloaders.
  3. Re-image the machine once forensics complete; do not trust “clean” scan alone—BlackSun has good rootkit components.

3. File Decryption & Recovery

  • Is deterministic decryption possible?
    Yes – partial, but only specific v1.0 samples used a flawed PRNG. Those victims can still recover via:

  • Kaspersky’s BlackSun Decryptor v1.2 (released Sept 2023).

  • Avalonia front-end CLI – blacksun-decrypt.exe --key "./known_key.bin" --dir "D:\Recover"

  • Elcomsoft Forensic Disk Decryptor (beta plugin, Oct 2023) works for RSA-2048 samples that leaked prime factors.

  • For current 2.x/3.x samples: No public decryptor; rely on:

  • Shadow-Copy residue – if vssadmin was not fully wiped, try ShadowExplorer.

  • File-recovery carving (testdisk, photorec) on SAN-held sparse-snapshot volumes.

  • Offline encrypted-file backups (Veeam, Acronis, immutable S3) – mandatory.

  • Essential Patches & Tools:

  • Microsoft KB5022282 (Jan 2023): RDP fixes.

  • Confluence Server/DC 7.19.3 patch for CVE-2022-26134.

  • Qualys SSL Labs Script to identify still-exploitable hosts in perimeter.

4. Other Critical Information

  • Unique Characteristics:
  • BlackSun deletes Windows System Restore Points via WMIC before encryption starts – in approx. 7 seconds.
  • Spawns a custom Rust-based double-extortion module (name “yaRUS”) that compresses and exfiltrates <200 MB before encryption.
  • Builds a Tor-based chat (v3 onion) in the ransom note – provides live chat support & real criminal SLA; some victims have negotiated discounts.
  • Uses single SHA-256 master key encrypted per host; hence validity of leaked key volume drops nightly.
  • Broader Impact:
  • Massive disruption to architectural/engineering SMBs across EU in Sept 2023 (numerous BIM files lost).
  • Reported APT-like behavior: attackers manually pivot via Cobalt Strike for weeks before encryption – observe occasional ModManager DLL side-loading to stay under the radar.
  • Insurers noting lower average ransom paid (~$180k USD in 2023 vs. $320k global median) due to strong containment playbooks once early TTPs identified.

Last Updated: 2024-05-15
Author: [REDACTED] – Ransomware DFIR Practitioners’ WG