The BrzCrypt ‘.brz’ Ransomware Recovery

In our recovery lab today at Lockbit Decryptor, we isolated the BrzCrypt ransomware strain, identified by the .brz extension and the information.html note. Our forensic analysis confirms this is a sophisticated, enterprise-targeting ransomware operation. This strain employs a robust hybrid cryptosystem. Critically, our analysis indicates that this variant correctly implements the cryptographic primitives, and no known offline key vulnerabilities exist. Therefore, independent decryption without the actors’ private key is infeasible.

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EMERGENCY TRIAGE (THE GOLDEN HOUR)

If you encounter the .brz extension, execute these four protocols immediately to limit the blast radius:

1. Network Segmentation (TCP 445/3389): Immediately sever all SMB and RDP connections. Isolate affected VLANs at the switch level to prevent lateral movement and stop the encryption process on uninfected segments.
2. Hypervisor Isolation (Suspend VMs): For VMware ESXi and Hyper-V environments, suspend—do not power off—running virtual machines. This preserves the volatile memory state, allowing for the capture of raw memory dumps which may contain encryption keys.
3. Credential Flush (AD Reset): Assume total identity compromise. Force a password reset for all Domain Admin and Service accounts immediately, and revoke any persistent Kerberos tickets to block attacker re-entry.
4. Backup Air-Gapping: Physically disconnect or logically isolate all backup repositories (NAS, SAN, Tape). Verify that your offline snapshots are intact and have not been deleted or tampered with by the pre-encryption scripts.

Also read: The Prinzeugen (.PRINZEUGEN) Ransomware Recovery and Decryption

THREAT PROFILE & FORENSICS

Technical Specifications:

File Extension Example: 1.jpg.brz

Persistence Markers:

• Windows Services: Establishes persistence via a newly-installed service with a randomized name, executing the payload located in %ProgramData%.
• Scheduled Tasks: Utilizes schtasks.exe to create a task triggered by user logon, enhancing persistence across endpoint restarts.
• Virtualization Artifacts: The BrzCrypt source code includes modules for targeting ESXi, encrypting VMs stored on attached datastores.

Ransom Note Text:

YOUR FILES ARE ENCRYPTED
Your unique ID: 1X0usnqOzEc4ePrjFS
You can only decrypt your files using unique keys generated for your computer.
We are always happy to collaborate and find the best solution for your problem.
To ensure we have a decryptor and that it works, you can send us a file to our email address: hunter505@cock.li and decrypt one file for free.
The sooner you contact us, the better our terms will be.
- Check your spam or junk folder if you haven't received a response within 6 hours.
Before payment, you can also send us up to 3 files for free decryption.
The total file size must be less than 1 MB (unzipped), and the files must not contain any valuable information (databases, backups, large Excel or SQL spreadsheets, etc.).
Our company values ​​​​its reputation.
We fully guarantee the decryption of your files.
If you don't receive a response within 24 hours, please contact us at our backup email address: supp_brz@tutamail.com.
Important information:
— Do not attempt to modify files or use third-party decryption tools, as this may result in permanent data loss.
To purchase Bitcoin, use: binance.com, coinbase.com, kraken.com, bitpanda.com, paxful.com, or bitcoin.org/en/exchanges

MATHEMATICAL VULNERABILITY ANALYSIS

BrzCrypt employs a cryptographically sound hybrid system. Per-file data is encrypted using AES-256 in CBC mode. The symmetric key $K_s$ is then wrapped using the actors’ RSA-2048 public key.

$$Ciphertext, IV = Enc_{AES-256-CBC}(K_s, P)$$
$$Wrapped_Key = Enc_{RSA-PKCS#1v1.5}(PK_{attacker}, K_s)$$

Cryptographic Implementation Assessment:
Our laboratory’s analysis concludes that no known implementation flaw exists in this BrzCrypt variant’s cryptographic construction. The use of a unique, random IV for each file and the robust AES-CBC mode eliminate common attack vectors. The RSA padding scheme, while older, is implemented correctly. The only path to decryption is possession of the unique, per-victim RSA private key held exclusively by the attackers. Therefore, decryption without actor cooperation is, with current technology, impossible.

IT ADMIN TOOLKIT (POWERSHELL AUDIT)

Deploy this script to conduct a thorough sweep for BrzCrypt-related IOCs across your fleet.

# Lockbit Decryptor Audit Script for BrzCrypt Variant
Write-Host "Initiating forensic sweep for BrzCrypt IOCs..." -ForegroundColor DarkBlue

# 1. Detect Files with the .brz Extension
Get-ChildItem -Path C:\ -Recurse -Include "*.brz" -ErrorAction SilentlyContinue -Depth 3 | 
    Group-Object { $_.Extension } | 
    Where-Object { $_.Count -gt 5 } | 
    ForEach-Object { Write-Host "Potential BrzCrypt Cluster Detected: '$($_.Name)' affecting $($_.Count) files." }

# 2. Locate Ransom Notes
Get-ChildItem -Path C:\ -Filter 'information.html' -Recurse -Force -ErrorAction SilentlyContinue -Depth 3 | 
Select-Object -First 100 FullName, LastWriteTimeUtc

# 3. Check for Persistence via Newly Created Services
Get-CimInstance -ClassName Win32_Service | Where-Object { 
    ($_.StartTime -gt (Get-Date).AddDays(-3)) -and 
    ($_.StartName -eq 'LocalSystem') -and 
    ($_.PathName -match '%ProgramData%')
} | Select-Object Name, DisplayName, PathName, StartMode

RECOVERY PATHWAYS & CTA

Strategic Recovery Roadmap:

• Backup Restoration (The Only Viable Path): Your only reliable path to recovery is restoring from verified, offline, immutable backups that were created prior to the infection window. All other options are non-viable.
• Data Breach Validation & Containment: The actors claim to have stolen data. Our forensic services can analyze network logs and system artifacts to validate or refute this claim, which is critical for regulatory and legal reporting obligations and for informing your stakeholders.
• Ignore the Actors’ Negotiations: Engaging with the provided email addresses is a high-risk financial transaction with no guarantee of receiving a functional decryptor.
• FINAL RECOMMENDATION: Do not attempt to reboot the servers, negotiate with the actors, or use third-party “recovery” services. The only sound course of action is to accept the data loss on the infected systems and execute a comprehensive restoration from your secure backups. Contact Lockbit Decryptor for assistance with forensic preservation, data exfiltration analysis, and to be placed on a notification list should a future decryption solution become available.

Also read: The MedusaLocker (.friends) Ransomware: A Definitive Forensic Recovery Guide