flowencryption

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The FlowEncryption ransomware concatenates the suffix “.flowencryption” to every file it encrypts (e.g., Budget_2024.xlsx → Budget_2024.xlsx.flowencryption).
  • Renaming Convention: A single pass is performed; no additional prefixes or random hex strings are placed in front of the original filename, so the only visual change is the appended extension. Encrypted folders also receive a marker file (see §3).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Public submissions began appearing on 6 March 2023, coinciding with spike in CERT-FI and ID-Ransomware reports. Minor iterative builds were still circulating through October 2023.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    – Phishing with ISO- and ZIP-attachments (“invoice”, “payment slip”) containing JavaScript or MSI wrapper that pulls the .NET payload from a Discord CDN URL.
    – Compromised RDP/VNC credentials followed by manual deployment of FlowEncryption.exe; brute force or prior info-stealer logs are commonly reused.
    – Exploits for public-facing software:
    • PaperCut NG/MF RCE (CVE-2023-27350, patched 8.3.8) used to write the launcher to C:\Windows\Temp\syshelp.exe.
    • RemotePotato0-style relay to elevate from local user to SYSTEM before encryption begins.
      – Peripheral vectors: GPO abuse once domain controller is breached, and PsExec to push flowenc-service.exe to multiple hosts in rapid succession (average encryption window < 40 min).

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Patch externally reachable services that FlowEncryption actors abuse—PaperCutNG/MF ≥ 22.0.5 or NG ≥ 21.2.9 (or switch to Mobility Print), and Windows March/2023 cumulative updates.
    • Disable SMBv1 and restrict RDP via GPO; enforce Network Level Authentication and 2-factor/Certificate-based auth for any remote-console access.
    • Application whitelisting (WDAC, AppLocker) to block unsigned binaries in %TEMP% and %APPDATA%.
    • Deploy robust e-mail filtering that drops ISO, IMG, JS, VBE, and MSI attachments from external senders by default.
    • Backup 3-2-1 rule with immutable/cloud snapshots (e.g., S3 Object Lock, Azure Immutable Blob) and periodically test restore. Lateral-movement speed means “same-day” backup loss is common if credentials are shared.

2. Removal

  • Infection Cleanup:
  1. Physically disconnect or L3-quarantine infected host; pull networking from domain controllers first to curb GPO deployment.
  2. Boot into Safe-Mode + Cmd or WinRE, rename FlowEncryption artefacts (flowenc-service.exe, FlowEncryption.exe, RunHelper.log, flowserv.pdb) to break scheduled restart.
  3. Check persistence:
    • Registry HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → ServiceHelper32
    • Scheduled Task \Windows\ModelHelper that launches "C:\PerfLogs\flowtask.exe -s"
  4. Scan with updated AM engine (Microsoft Defender 1.393+, ESET 27107h, Sophos 5.0.2+) to remove remains; VirusTotal hash family identifier: sha-256 4f8ad7…
  5. Examine LSA/NTDS dumps for credential theft, revoke all local/domain passwords if evidence of Mimikatz/BCrypt dumping.

3. File Decryption & Recovery

  • Recovery Feasibility: Files are encrypted with AES-256 in CBC mode (16-byte static IV) per file; the AES key is RSA-2048-encrypted with a hard-coded public key embedded in the binary. The malware authors hold the private key offline; there is no known flaw in their key handling as of this writing.
  • Free decryption therefore impossible—no public decryptor exists.
  • Brute-forcing the 2048-bit RSA key is computationally infeasible; immutable offline backups are the only reliable path.
  • Essential Tools/Patches: Kaspersky RannohDecryptor, Emsisoft STOP-Decryptor, and similar utilities do NOT support *.flowencryption. Victims should leverage backup software or specialist incident-response teams to rebuild instead of paying the ransom.

4. Other Critical Information

  • Additional Precautions:
    – Inside every hit directory the malware creates RESTORE-FLOW-FILES.txt (TOR-based negotiation link & “flow-support” e-mail). Launching the ransom note triggers an embedded PowerShell snippet that attempts to exfiltrate computer-name, user, and file-count to a Telegram bot; block outbound connectivity to api.telegram.org to stop this beacon.
    – Version 2 builds in Q4-2023 included a buggy wiper routine that deletes *.bak, *.vhd, *.vlbk regardless of payment—whether this is intentional or collateral damage remains unclear; early containment is critical.
  • Broader Impact: The group’s post-exploitation scripts pivot through Azure AD Connect staging accounts; two reported victims saw Active Directory forests fully tarnished, requiring complete rebuild (1800 endpoints). DFIR telemetry suggests the operators are part of the same RaaS affiliate pool previously pushing Zeppelin and Rorschach, reusing their Cobalt-Strike watermarks (“vendetta74”, “killemoff”) and Malleable-C2 profile “firefox-jet ”. Expect rapid, high-pressure countdown timers (72 h) followed by public auction on Breach-Forums if ransom unpaid. Maintain incident-response retainers and ensure DoD-compliant secure-hardening baselines are applied to virtualisation and hyper-converged environments where organizations store their “last-resort” backups.

Use the above profile to update your incident-response playbooks and ensure SOC teams have detection rules in place for the IOCs and behavioural signatures described. Early isolation and immutable backups remain the single most effective defence against FlowEncryption. Stay safe out there.