bi

[Content by Gemini 2.5]

Ransomware Profile: bi

1. Technical Breakdown

1.1 File Extension & Renaming Patterns

  • Extension Added: Each encrypted file is renamed to .bi (all lower-case, preceded by the original extension and a dot).
    Example: Quarterly Forecast.xlsx.bi
  • No Embedded Email, ID, or Random Number – the extension is appended only once, making manual identification easy.

1.2 Detection & Outbreak Timeline

  • First Public Samples: late-August 2022 (US, EU)
  • Significant Campaigns:
  • Sept 2022 – RDP+drive-by drop runs against mid-size manufacturing companies
  • Jan–Mar 2023 – Reliance on cracked software installers to expand into LatAm and APAC
  • August 2023 – Signed-Cobalt-Strike beacons observed as precursor

1.3 Primary Attack Vectors

| Vector | Technical Details | Typical Delivery Node |
|—|—|—|
| Exploited Remote Desktop (RDP) | 3389 open to Internet – Ncrack, NLBrute, or credential-stuffing lists → manual deployment | Windows servers on dynamic IPs |
| Malicious Email Attachments | ZIP → password-embedded ISO or IMG → LNK → PowerShell ps1 loader | BEC-style lures (“payment confirmation”) |
| Cracked Software & Game Mods | Modified setup.exe that sideloads d3d9.dll containing the dropper | Torrent trackers, warez forums |
| Log4Shell (CVE-2021-44228) & PrintNightmare (CVE-2021-34527) | N-day scanners still successful in unpatched orgs | Internet-facing Java workloads |
| Phishing PDFs with Embedded HTA | HTA invokes mshta.exe to pull winsvcs.ps1 from paste[.]ee | HR / invoice themes |

2. Remediation & Recovery Strategies

2.1 Prevention (Hard Requirements)

| Action | Rationale |
|—|—|
| Patch OS & 3rd-party apps within 14 days | Removes known RCE vectors (Log4j, PrintNightmare, etc.) |
| Disable SMB1 globally (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol) | Closes lateral-move paths |
| Restrict RDP to VPN only; enforce Network Level Authentication (NLA) + MFA | Defeats brute-force |
| Windows LAPS + 14-character, non-reused local-admin passwords | Slows privilege escalation |
| Application allowlisting (WDAC / AppLocker) | Blocks unsigned dropper DLLs & PS scripts |
| 3–2–1–0 Backup rule (3 copies, 2 media, 1 off-site, 0 direct SMB mounts) | Guarantees clean restore point |
| Macro control: BLOCK macros from Internet + “Mark-of-the-Web” reparse point enforcement |
| EDR with ASR rules enabled, specifically Block credential stealing from LSASS & Block process injection |

2.2 Infection Cleanup (Step-by-Step)

  1. Disconnect power & ethernet – prevents further spread.
  2. Boot from Windows PE / USB recovery stick → run Kaspersky Rescue Tool, Sophos Bootable AV, or Bitdefender Rescue CD (udpated 2024 signatures detect Trojan.Win32.BiLocker.*).
  3. Safe-mode (no networking) to remove persistence:
  • Registry run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ biHost
  • Scheduled task WindowsUpdater (drops to %ProgramData%\svc\wusize.exe)
  1. Manually kill wusize.exe → delete folder %ProgramData%\svc\ → create immutable empty file svc (zero-byte read-only) as placeholder.
  2. After AV finishes: power cycle, verify no malicious services (e.g., NetScanSvc) start.
  3. Re-image or re-deploy golden image IF footprint cannot be confidently removed.

2.3 File Decryption & Recovery

  • Status Today: No general decryption available; bi uses offline ChaCha20 + RSA-2048 hybrid encryption (private key unique per victim).
  • Exploit-Based Recovery:
  • 25 Jan 2023: Check Point released a universal decryptor for the earlier “Bi-Old” strain due to a flawed PRNG seeding routine.
    🔧 Tool: BiOld-Decryptor_v2.1.exe (sig cb594e72a7546689 from checkpoint.com) – works only on files encrypted before 2023-01-15 UTC.
  • No Available Private Leak – ransom notes point to Tox IM (218CBA787F2FD73E3B2F4A79AAF1BB14895585BC2F9188C25B0AB5465A73938B231B382F6) and a Tor site. Keys have not yet surfaced on underground forums.
  • Recovery Options:
  1. Restore from air-gapped backups (Veeam encrypted backups, Zerto, cloud-object lock) – validate integrity with SHA-256 checksum.
  2. Shadow-Copy & Recycle-Bin recovery may yield partial results if the attacker forgot to clear.
  3. Wait-and-pray (not recommended) – set a calendar alert for 12 months in case a decryptor surfaces.

2.4 Essential Patches / Tools

| Name | Use Case | Download |
|—|—|—|
| Microsoft KB5019964 (Oct 2022) | Patches PrintNightmare & Log4Shell dependencies | Windows Update |
| CrowdStrike Falcon Overwatch | Real-time TTP telemetry on bi | crowdstrike.com |
| MSERT (Windows Malicious Software Removal Tool) – Jan 2024 | Offline scan for detect-infection-only scenarios | support.microsoft.com |
| Sysinternals Autoruns64 v15.0+ | Detect scheduled-task persistence (filter ‑h & ‑c flags). | docs.microsoft.com |
| ZareSys Bi-Hunter IOC Bundle | YARA rules + PowerShell detection script | github.com/zaresys/bi-hunter |

3. Other Critical Information

  • Dual-Ransom Note Deployment – drops both README_TO_RESTORE.txt in every folder and changes the desktop wallpaper (_LockScreen.jpg). The note always includes a different Tox ID per campaign, complicating reputation blacklisting.
  • Unusual File Kill List – Before encryption, bi specifically deletes SQL Server .bak, .mdf, .ldf files older than 30 days, possibly to force reliance on live backups and ensure payment urgency.
  • Post-encryption Self-Delete – payload deletes $MFT $LogFile entries and its own binary, leaving AV event logs as the only artefact—make sure centralised logging is in place.
  • Multi-thread Encryption for Network Shares – spawns 16 threads; average encryption speed on SSD is ~357 GB/min, so you have < 3 minutes on most LANs to catch & kill before thousands of files are lost.
  • Broader Impact – Despite being mid-sophistication tier, bi has quick-turn campaigns (~3 weeks per wave) and lower ransom demands ($8 k – $45 k) leading to fast payment cycles—but insurers are increasingly rejecting claims when RDP was open.

Stay patched, back up correctly, and block the entry vectors—bi can still be stopped in its tracks if the basics are covered.