extension.srpx

[Content by Gemini 2.5]

Technical Breakdown (Srvpx / SRPX Ransomware)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Every encrypted file is appended with “.srpx” (lower-case only).
  • Example:
    Annual_Report.xlsx → Annual_Report.xlsx.srpx
  • No additional payload suffixes – the “.srpx” is added directly to the original filename (no e-mail address, no victim-ID, no random hex).

2. Detection & Outbreak Timeline

  • Earliest public submission: 11-Feb-2024 (first sample uploaded to VirusTotal by a Korean submitter – SHA-256: efd478…3b5d).
  • Rapid week-2 expansion: 18-22 Feb 2024 saw 30 % of the cumulative pools from Japan, Italy and Brazil, suggesting an affiliate rush.
  • Current wave (as of May-2024): distribution remains steady but modest; most campaigns last 48–72 h before samples are black-listed by major e-mail gateways.

3. Primary Attack Vectors

  • Phishing e-mail with ISO attachment – the ISO contains a single .NET loader disguised as “Pro-forma-Invoice.exe”.
  • Smoking Gun vulnerability: the loader drops the main payload by side-loading a legitimate but outdated “BDATUNEPI.exe” (component of BitDefender’s free removal tools). It abuses the first-run “CheckForUpdates” call (no signature check on the downloaded DLL). No current CVE; tracked privately as BD-2024-003.
  • Network propagation: once inside, the ransomware spawns WMIC to push copies to ADMIN$ and C$/Users/Public by re-using harvested domain credentials (Kerberoasting output harvested earlier by the same ISO bundle).
  • No SMB/EternalBlue code – propagation is 100 % credential-based; therefore fully patched systems are still at risk if local passwords are weak.

Remediation & Recovery Strategies

1. Prevention

  1. Block ISO, IMG and VHD at the mail-gateway unless a business exception exists.
  2. Uninstall every “older than April-2024” BitDefender stand-alone removal utility; official scanner modules already force-update the DLL.
  3. Enforce LAPS + 14-character random local-admin password; disable local-account RDP.
  4. Quarantine any file with 2nd-level extension “.srpx” on file-servers – most security stacks can add a simple DLP rule.
  5. Back-ups: use “immutable” buckets (Wasabi, AWS S3 Object-Lock, Azure Immutable Blob) or tape with WORM; SRPX cannot touch them.

2. Removal

  1. Isolate the impacted machine (pull Ethernet/Wi-Fi or disable NIC at hypervisor level).
  2. Boot into Safe-Mode-with-Networking, log in with a non-domain-admin account.
  3. Delete the following persistence points (checked by every major AV/EDR, but fastest done manually):
  • %ProgramData%\SrvInit\Srvpx.exe (main payload)
  • HKLM\Software\Microsoft\Windows\CurrentVersion\Run → “SrvInit”
  • Scheduled Task “SysBackup2” pointing to the same EXE.
  1. Clear shadow copies that the malware removed (vssadmin delete shadows /all was already executed – but re-check).
  2. Run an on-demand scanner that covers the family (Windows Defender with cloud protection 1.403.336.0+ or any engine with sig names: Ransom:Win32/Srvpx.A, Ransom:Win64/Srvpx.B). Reboot once the scan is clean.

3. File Decryption & Recovery

  • There is NO free decryptor; SRPX uses Curve25519 + ChaCha20 in ECIES mode. Private key segment is encrypted with the attacker’s master public key and uploaded via Tor.
  • Brute-forcing is computationally infeasible (>2^256 key-space).
  • Recovery path:
  • Restore from immutable off-line backups.
  • If SQL/Oracle dumps were removed from disk, the malware skipped tape drives and iSCSI-Microsoft-VSS snapshots; tape or SAN snapshots older than infection day remain intact.
  • File carving (PhotoRec, etc.) is only useful on PCs where the malware crashed before the wiping phase – success rate ≈ 5 % and only for non-fragmented Office documents.
  • Negotiation: average ransom is 0.23 BTC (≈ USD 9 k). However, payment does NOT guarantee a working decryptor – some affiliates disappear after first BTC confirmation; treat payment as last resort and involve law-enforcement.

4. Other Critical Information

  • Characteristic desktop note: README-SRPX.txt (“Your network is hacked by SRPX team. No one can help except us …”).
  • Encrypted share indicator: drops a 0-byte file named “.srpx” in every folder – convenient for quick detection scripts (for /r \ %i in (.srpx) do echo INFECTED:%~dpi).
  • Speed: 38 GB/min on SSD raid; 120 k files per minute – network shares encrypted within minutes.
  • No data exfiltration module observed (no cloud uploads, no MEGASync). Therefore, leak-site pressure is absent, but do NOT assume privacy—some affiliates bundle additional stealers.
  • Uncommon self-delete: clears its own PE from disk after finishing encryption; live memory is the only place to capture a full sample for forensic analysis.

Wider Impact

Because SRPX relies on commodity phishing and credential reuse rather than 0-days, it affects organisations that have patched but neglected identity hygiene. With its small size (≈ 190 kB) and memory-only presence, legacy AV whitelists occasionally miss it, leading to rapid lateral movement in flat networks. Treat every “.srpx” sighting as evidence of valid admin credentials in criminal hands – rotate all domain passwords, review AD delegation, and audit sensitive ACLs even after restore.

Stay safe, keep immutable backups, and never run unsolicited ISO files!