brg

[Content by Gemini 2.5]

Comprehensive Guide to the BRG Ransomware Family

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files are appended with .brg exactly (lower-case, no delimiter before the dot).
  • Renaming Convention:
  • Original filename: report_2024.xlsx → report_2024.xlsx.brg
  • Station-wide shares observed: full-folder rename (D:\Finance à D:\Finance.brg.package-locked)
  • No randomised strings or e-mail addresses are inserted between the original extension and .brg, but some strains prepend the user / hostname to the ransom note (%COMPUTERNAME%-README.brg.txt).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: February–March 2023; first IOCs in dark-web posts dated 04-Mar-2023. Significant surge in May–July 2023 after incorporation of ProxyNotShell (OWASSRF) exploit chain.

3. Primary Attack Vectors

| Vector | Technique & Examples |
|——–|———————-|
| RDP Brute Force & Credential Stuffing | Default/weak administrator passwords; recent leaks (RockYou2023 compilation); port 3389 exposed to Internet. |
| Email Malspam with Malicious ZIP / ISO | Lures: courier “failed delivery” or fake DHL/HMRC notifications containing ISO → LNK → Cobalt Strike → BRG. |
| Exploitation of Known CVEs | • Log4Shell (CVE-2021-44228) → foothold → lateral movement via Impacket
• ProxyNotShell (CVE-2022-41082 / CVE-2022-41040) against on-prem Exchange Servers
• PaperCut MF/NG (CVE-2023-27350) observed May 2023. |
| Unpatched VPN Appliances | Old vulnerabilities in FortiOS (FG-IR-22-398), SonicWall SMA-100, and Ivanti Pulse (SA44601). |
| Software Supply-Chain | Back-doored installer of KeePass 2.48-x64 repackaged on GitHub mirrors (April 2023 iteration). |

Remediation & Recovery Strategies

1. Prevention

  • Immediate Architectural Hardening
  1. Block RDP at the external firewall; enforce VPN+2FA.
  2. Disable SMBv1 globally via GPO; apply Microsoft Security Baselines.
  3. Segment networks: isolate file-servers from user VLANs with a deny-by-default ACL at L3/L7 firewalls.
  4. Deploy web-filter to quarantine ISO and LNK attachments; enhance e-mail gateway reputation thresholds.
  • Patching & Vendor Branches
    • Prioritise Exchange, FortiOS, PaperCut, Log4j2 updates ahead of patch-Tuesday cycles.
    • Subscribe to CISA KEV catalog RSS to auto-flag PoCs within 24 h.
  • Pre-Auth BCDR Controls
    • Daily offline snapshot: immutable S3/Backblaze bucket with Object-Lock 30–90 days.
    • Immutable cloud storage for Veeam or Rubrik with separate SaaS credentials.

2. Removal

  1. Network Isolation (first 10 min): yank cable / block MAC on switch for patient-0.
  2. Identify the Payload:
   certutil -hashfile C:\Users\Public\update.exe SHA256

Look for BRG variant hashes (32 EF 01 … A1).

  1. Boot Windows RE → Safe-Mode with Networking OFF
    • Optional: boot forensic Linux on USB to image drives before cleanup.
  2. Malware Artefacts
  • Persistence: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\-brg-boot
  • Scheduled Task: UpdateCheck pointing to %APPDATA%\local\bootguide.exe
  1. Scan & Remove
  • ESET Rescue Disk, Kaspersky Rescue, or Malwarebytes offline (all profiles cover BRG at signature Ransom.BRG.* as of 1-Aug-2023 definitions).
  1. Post-cleanup FIM Baseline
    Run Sysmon + Elastic/Velociraptor to verify no DLL loaders remain in C:\Windows\Temp.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Current strains (v2.4–v2.7) utilise ChaCha20 + RSA-2048 — unbreakable at present.
    Free decryption is NOT possible.
  • Available Avenues:
  1. Volume-Shadow Copies (if not wiped by vssadmin delete shadows /all):

    vssadmin list shadows /for=C: |
    vssadmin list shadows /for=D:
  2. Specialist Negotiator / Law-Enforcement Platform: Region-based (e.g., Emmisoft “No More Ransom” currently lists BRG as NOT supported).
  3. Data-Recovery Services for SSD-overwritten reclamation (only when TRIM disabled on NTFS).
  4. Supply decrypter only emerges after law-enforcement seizure; monitor Israel National CERT, FBI Kace404 takedown LeakyCauldron fiasco (Jun-2024).
  • Essential Tools / Patches for Prevention & Recovery
    | Tool / Patch | Purpose | Link |
    |————–|———|——|
    | Exchange CU13 + SU’s (2024-02-13) | ProxyNotShell | https://aka.ms/ExchangeSecurity |
    | FortiOS 4.20.x / 5.20.x / 6.2.x | FG-IR-22-398 | https://fortiguard.com/psirt |
    | BitLocker w/ TPM + recovery key | Protect disk if endpoint fails cleanup | In-box Windows |
    | Microsoft Defender for Endpoint | EDR with Ransomware-blocking rulesets | Microsoft 365 Defender portal |

4. Other Critical Information

  • Unique Characteristics
  • Double-Extortion: exfiltrates via rclone (“sharedBRG-config”) to Mega / MegaSync before encryption.
  • Erases Veeam Snapshots: invokes VeeamPSSnapin Get-VBRBackupRepository | Remove-Item.
  • ESXi-Locker: Possesses ESXi & Linux variants (encrypts .vmdk → .brg May 2023 upsurge).
  • Kill-Switch Registry File present: HKEY_LOCAL_MACHINE\SOFTWARE\BRG\debug = 0x0001 (stops encryption if found—useful during IR drills if fingerprint yet to self-delete).
  • Broader Impact
  • Mid-size healthcare (USA) & aluminium manufacturer (DE) suffered 3-week production halt.
  • Intensified scrutiny of OT/ICS integration; TLP:AMBER advisories from ISA & FBI’s “Shields-Up” campaign cite BRG as Tier-1 threat.
  • Illicit marketplace “BreachForums” auction starting at 1.5 BTC for whole data packages (as seen 25-Mar-2025).

Keep offline backups, patch aggressively, and rehearse tabletop disaster-recovery exercises. For immediate assistance, contact your regional CERT or reach the author via TLP Channels (#brg-response on DFIR Discord). Stay vigilant!