The MORTAR Ransomware Decryptor and Recovery

In our recovery lab today at Lockbit Decryptor, we isolated the MORTAR ransomware strain, identified by victim-specific ID extensions (e.g., .4RcrXfvVksS5ACA) and the README-[ID].txt 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 victim ID extensions, 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: document.pdf.4RcrXfvVksS5ACA

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 MORTAR source code includes modules for targeting ESXi, encrypting VMs stored on attached datastores.

Ransom Note Text:

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| What happened to your files?
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We breached your corporate network and encrypted the data on your computers. The encrypted data includes documents, databases, photos and more - all were encrypted using a military grade encryption algorithms (AES-256 and RSA-2048). You cannot access those files right now. But don't worry!

You can still get those files back and be up and running again in no time.

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| How to contact us to get your files back?
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The only way to restore your files is by purchasing a decryption tool loaded with a private key we created specifically for your network.

Once run on an effected computer, the tool will decrypt all encrypted files - and you can resume day-to-day operations, preferably with better cyber security in mind. If you are interested in purchasing the decryption tool contact us at hxxp://hpo7htcpddfanilknttsymttzfr4usxwjycjpazkleggnvry5bngszyd.onion.

!IMPORTANT!
TO RESTORE YOUR FILES CONTACT US VIA TOR BROWSER

WEBSITE: hxxp://hpo7htcpddfanilknttsymttzfr4usxwjycjpazkleggnvry5bngszyd.onion
USERNAME: sid
PASSWORD: 4RcrXfvVksS5ACA

BACKUP LINK TO SUPPORT TEAM: hxxp://hpo7htcpddfanilknttsymttzfr4usxwjycjpazkleggnvry5bngszyd.onion
!!!!!!!!!!!

MATHEMATICAL VULNERABILITY ANALYSIS

MORTAR 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 MORTAR 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 MORTAR-related IOCs across your fleet.

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

# 1. Detect Files with Random ID Extensions
Get-ChildItem -Path C:\ -Recurse -ErrorAction SilentlyContinue -Depth 3 | 
    Where-Object { $_.Extension -match '^\.[a-zA-Z0-9]{15}$' } | 
    Group-Object { $_.Extension } | 
    Where-Object { $_.Count -gt 5 } | 
    ForEach-Object { Write-Host "Potential MORTAR Cluster Detected: '$($_.Name)' affecting $($_.Count) files." }

# 2. Locate Ransom Notes
Get-ChildItem -Path C:\ -Filter 'README*.txt' -Recurse -Force -ErrorAction SilentlyContinue -Depth 3 | 
Where-Object { (Get-Content $_.FullName -Raw) -match 'military grade encryption' } | 
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 Tor site or credentials 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.

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