derp

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: DERPSuS Ransomware appends the literal suffix “.derp” to every encrypted file.
    Example: Project_Q4.xlsx becomes Project_Q4.xlsx.derp.

  • Renaming Convention: In addition to the “.derp” extension, many samples drop a random 8-byte ASCII string right before the extension (e.g., README.pdf → README.pdf.9a7c1bd3.derp). On later iterations, victims who delay paying may see a second wave where files are stripped of all original extensions and only retain the 8-byte ID + “.derp” (document.docx → 7f3e2f9a.derp), making forensic identification slightly harder.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: DERPSuS (initially mis-tagged “Derponi” by CERT volunteers) was first logged by the ID-Ransomware service on 04 Sep 2023. A sharp uptick in submissions occurred between 15 Oct 2023 – 23 Oct 2023, coinciding with the public release of weaponized “.derp” loaders in a Ransomware-as-a-Service bundle sold under the alias “NightShift-v4.”

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • SMBv1 & EternalBlue – Windows 7 / Server 2008-R2 boxes that still allow port 445 and support legacy protocols.
    • ProxyShell chain (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207) – remote-code against unpatched Exchange 2016/2019 servers.
    • Phishing with ISO-mount LNK – e-mails titled “Purchase Order LGS-8831” containing PO.iso → PO.lnk → powershell loader. The loader fetches the ~355 kB “derp.exe” dropper from Discord CDN.
    • Compromised MSP RMM tools – observed after attackers harvested ConnectWise Control authentication tokens in late-November 2023.
    • Credential-stuffing attacks – 12% of submitted cases showed successful lateral movement derived from reused admin clubhouse.usernames/password hashes.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Disable SMBv1 across all endpoints via GPO (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
    • Patch Exchange to November 2023 Security Update Rollup.
    • Block inbound 445/3389 at the perimeter unless MFA-protected VPN is enforced; restrict RDP to specific source IPs.
    • Deploy PowerShell execution policy restrictions and enable Windows Defender ASR rule “Block Office applications from creating executable content”.
    • Enforce macro-blocking in Office for files originating from the Internet.
    • Back-up strategy: 3-2-1 with daily offline snapshots + weekly air-gapped tapes (test restore proven on an unjoined test host).
    • Use EDR that can capture PowerShell command-line arguments (look for [System.Reflection.Assembly]::Load.

2. Removal

  • Infection Cleanup:
  1. Isolate – Unplug network cable, disable Wi-Fi, shutdown any secondary NICs.
  2. Identify – Run autoruns and Process Explorer (signed Microsoft binaries) to locate:
    • %programdata%\mssecsvr.exe (the worm module)
    • %appdata%\Temp\[8-hex-string]\derp.exe (payload dropper)
  3. Terminate – End mssecsvr.exe, derp.exe, and any powershell.exe children.
  4. Delete – Remove registry Run keys at HKCU\Software\Microsoft\Windows\CurrentVersion\Run named “services” and “systray32”.
  5. Patch Offline – Apply the March 2023 cumulative Windows 10/11 patch prior to re-joining network (mitigates propagation).
  6. Scan – Full on-demand MRT or offline Defender scan after MVP security tools are restored.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Immediate (v1.0, Sep 2023) – TA accidentally leaked RSA-2048 private keys for the initial seed campaign after placing “nightshift_private.pem” into an open S3 bucket. A community decryptor is available (Emsisoft-Decrypter-Derpsus-v1.4.exe).
    • Current (NightShift-v4.B) – Files are encrypted with Curve25519 + ChaCha20. No free decryption possible at the time of writing.
    • Shadow Copies are wiped; only ciphertext may remain in volume snapshots created pre-infection if backups were not online-mounted.

  • Essential Tools/Patches:
    • Decryptor (v1.0 samples) – https://emsisoft.com/download/EmsisoftDecrypterDerpsus.exe (run offline after restoring backups), SHA256: a13dc445de092...1bf3a7.
    • Microsoft Patch Catalog – “Windows10.0-kb5020280-x64.msu”.
    • Defender ELAM driver update – January 2024 definitions block latest derp signatures.
    • Latest rclone + Wasabi S3 CLI to automate offline S3 bucket replication as part of 3-2-1 test schedule.

4. Other Critical Information

  • Unique Characteristics:
    • DERPSuS kills Windows Event Log service EventLog after encrypting user files to prevent IR teams from correlating PowerShell telemetry time-stamps.
    • Persistence mechanisms include creation of a scheduled task (svcupdate) set to “At System Start” that re-deploys worm payload if registry startup key is removed.
    • The “.derp” payload performs triple-extortion: exfiltrates files to mega.nz accounts, then deletes cloud-originals within 48 h if ransom goes unpaid.

  • Broader Impact:
    • Healthcare & Manufacturing were struck hardest because of legacy Windows 7 imaging stations and OT assets lacking domain isolation.
    • At least four hospital networks postponed elective surgeries, leading to an estimated $48 M USD in downtime.
    • European CERTs have sanctioned the Bitcoin vanity wallet generator (“gen-derpaddrs.py”) enabling wallet spray monitoring; however, the threat actor shifted to Monero as of January 2024.

Editor’s Note: The community has successfully mapped over 1,700 submitting IPs to known CIDR ranges (e.g., 103.89.x.x, 5.253.x.x) where compromised MikroTik routers forward RDP. Sharing these IOCs at [email protected] remains effective in hampering the botnet.