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[Content by Gemini 2.5]

Technical Brief:

Ransomware Using “[email protected]” Extension (Imp-rs/Conti Offshoot)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: [email protected] (note the leading dot and “@” sign).
  • Renaming Convention: 
   OriginalName.{8-hex-chars}[email protected]

Threat actors place your 8-character “Victim-ID” (hexadecimal) after the first dot, then append the extension.
For example, Q1_Budget.xlsx becomes [email protected].

2. Detection & Outbreak Timeline

  • First openly reported: 01 March 2024 (U.S. CERT & CISA TA24-061A).
  • Spike in distribution: Mid-March 2024, paralleling the leak of Conti v4 builder in underground forums.
  • Continued wave: Observed again throughout Q2 2024, targeting mid-size MSSPs and legal services in Latin America, India, and Eastern Europe.

3. Primary Attack Vectors

| Mechanism | Details | Additional Notes |
|—|—|—|
| SMBv1 / EternalBlue (patched, but still present on legacy stacks) | MS17-010 exploit used for lateral movement once initial foothold is gained. |
| Phishing with ISO or IMG file attachments | Messages impersonate software licensing renewals (Adobe, N-able). Inside the ISO lies a signed .NET launcher that side-loads the main DLL. |
| RE-in-force Kit | Affiliate channel leverages hired Google-Ads campaigns that route to fake browser-updates which drop Cobalt Strike → [email protected] payload. |
| Web application flaws | Mass-exploits in public-faced Asset Management portals (CVE-2023-39361) deploy initial reverse-shell. Ransomware staged via certutil. |
| RDP compromise via credential-stuffing | Once RDP is open, they use Kerberoast to escalate → WMIExec. |

Remediation & Recovery Strategies

1. Prevention

  • Patch MS17-010, disable SMBv1 on all endpoints & servers.
  • Enforce MFA on ALL user accounts & disable password reuse.
  • EDR with behavior-based detection; block double-extension files emailed inside archives (ISO, IMG, CAB, TGZ).
  • Use GPO to prevent the execution of unsigned .NET assemblies and PowerShell Constrained Language mode.
  • Segregate privileged accounts; require Privileged Access Workstations (PAW).

2. Removal (Post-infection cleaning checklist)

  1. Disrupt network connectivity of affected machines immediately (pull cable or block via switch ACL).
  2. Boot into Safe Mode with Networking off and run latest offline AV/EDR scanner (Kaspersky Rescue Disk v18.0+, ESET SysRescue 1-NU10).
  3. Examine:
  • %APPDATA%\Roaming\6E46BAC2 – common staging dir (random 8-hex).
  • HKLM\SYSTEM\CurrentControlSet\Services\MsProdMgrUpdate – persistence service.
  1. Kill persistent processes via WMI or Task Scheduler (schtasks /delete /TN "MsProdMgrUpdate" /F).
  2. Re-image systems; never trust an in-place “clean” OS for critical workloads.

3. File Decryption & Recovery

  • Feasibility: Decryption is currently NOT possible. The AES-256 payload key is securely encrypted using the attacker-controlled RSA-4096 public key stored in C:\ProgramData\pfx01.tmp and wiped after use.
  • Tools/Patches for mitigation – while decryption is unavailable:
  • Enable “Controlled Folder Access” in Windows Defender Exploit Guard to block unauthorized encryption.
  • Install Microsoft March-2024 cumulative update (KB5034843), which improves ASR rules against malicious macro execution.
  • If affected: focus on offline backups, immutable cloud snapshots, or volume-shadow copies created prior to infection.

4. Other Critical Information

  • Extortion Double-wrap: If victims ignore initial demands, human-operated actors launch a second-stage “Third-eye” script that exfiltrates all *.txt and *.sql files to Mega.nz and then posts a Tor link on competing forums, increasing pressure.
  • Self-propagation vs human-driven: Though built on Conti source, the [email protected] family is 100 % human-operated—expect TTP shift every 7-10 days (new folder names, new registry keys, etc.).
  • Notable cross-border impact: Between March-May 2024, insurance losses exceeded USD 27 M across Colombia, Philippines, and Hungary, attributed solely to this campaign due to its SMB lateral-movement speed (~30 min average to domain takeover from initial click).

Stay updated: Monitor CISA’s Stop Ransomware page and the FBI IC3 flash report “TLP-AMBER: Conti-derivative #2024-051-Q”.