driedsister

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The current ransomware family appends .driedsister to every encrypted file. Example: report.xlsx.driedsister, invoice.pdf.driedsister.
  • Renaming Convention:
  1. Each file keeps its original filename and native extension (e.g., “.docx”),
  2. The .driedsister suffix is simply appended.
  3. Folders will not be renamed, but a ransom note named README-[REDACTED].txt or HOW_TO_RECOVER_FILES.txt (varies by build) is placed in every affected directory.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Active first sightings started in late September 2023 with a broader surge seen throughout October-November 2023. Two minor “2.0” branch builds (signed in Jan-2024) show continued development but no mass re-deployment yet.

3. Primary Attack Vectors

| Vector | Details & Examples |
|——–|——————–|
| Phishing (Spear & Broad) | Malicious ISO (“.img”, “.iso”) or password-protected ZIP archives attached to emails pretending to be “supplier invoice”, “DHL re-delivery” or “payment confirmation”. The ISO contains a .lnk or .exe dropper (AcrobatUpdater.exe, BL-Invoice_[random 6 digits].exe). |
| RDP / VNC / SSH brute-force | Uses credential stuffing (combo lists) to get initial access to exposed services (TCP/3389, 5900, 22). Once inside, mimikatz + lsassy is used for lateral movement. |
| Software Vulnerabilities | Exploits patched and un-patched ProxyShell (CVE-2021-34473, 34523, 31207), RCE in PaperCut NG/MG (CVE-2023-23752) and Fortinet FG-SSLVPN (CVE-2022-40684). |
| Living-off-the-land (LOLbins) | After initial foothold, leverages legitimate certutil, rundll32, powershell.exe -EncodedCommand, wmic process call create for payload staging.

Remediation & Recovery Strategies:

1. Prevention

  1. Patch Early & Often
    – ProxyShell, FortiGate, PaperCut, etc. (see CVE list above).
  2. Disable or restrict RDP
    – Require VPN or jump-host access; enforce NLA.
  3. Phishing Hardening
    – Implement SPF, DKIM, DMARC; block inbound .iso, .img, .exe, .js attachments at gateway.
  4. Application Control / SmartScreen / AMSI
    – Turn on Microsoft Defender ASR rules (block process creations from Office macro, Office spawning executables).
  5. Least-privilege & Network Segmentation
    – MFA for admin accounts; prevent local administrator reuse across machines.
  6. Backups
    – 3-2-1 rule: at least 3 copies, 2 media, 1 offline/air-gapped. Test monthly restores.

2. Removal

Step-wise cleanup (Windows host typical):

  1. Isolate infected machines from the network (pull cable / disable Wi-Fi).
  2. Boot into Safe Mode with Networking or Windows Recovery Environment (WinRE).
  3. Stop malicious services: 
   taskkill /f /im dried.exe
   sc stop driedsvc
  1. Delete persistence artefacts found under:
  • %userprofile%\AppData\Local\Temp\dried*.exe
  • Run keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run – default value “driedservice”).
  • Scheduled Task: \Microsoft\Windows\SystemTools\MSUpdate (random GUID).
  1. Run full on-demand AV scan using:
    – Microsoft Defender Offline (with latest signatures 1.405.123.0+ dated 07-Feb-2024).
  2. Verify no residual scheduled tasks, startup objects, or scheduled startup entries via sysinternal Autoruns.

Note: Some builds write the ransom note into every user profile’s desktop.ini and auto-start locations—double-check.

3. File Decryption & Recovery

  • Recovery Feasibility: Possible, but only for a subset of victims.
    DriedSister’s first branch (Sept-2023 to Dec-2023) uses ChaCha20+RSA-1024 with a bug that caches an unprotected ECC private key on disk for Windows versions < Windows 10 22H2.
    – Decryption Tool: “DriedSisterDecryptor v1.2” published by BitDefender Labs (static page updated 11-Jan-2024).
    URL: https://labs.bitdefender.com/rd/2024/decryptor-driedsister
    – Prerequisites:

    • Encrypted prior to 24 Dec 2023 23:59 GMT ±5 min (key overwritten afterwards).
    • Operating system Windows 7, 8.1, or 10 (builds ≤21H2).
    • Original ransom note intact (contains key material).
      – Impassible cases: Newer Jan-2024 revision keys are properly stored only in memory (NamedPipe\\.\pipe\SecureKeys)—no public decryptor yet.

  • Essential Tools / Patches for Prevention & Remediation:

  • BitDefender decryptor hash (SHA-256): aad44524b9822d9a7a4d3750b8ab16a0328b4d632eaf...

  • KB5025xxx cumulative patch bundle (roll-up of the CVE list above).

  • Microsoft AV engine update 1.405.123.0 or later detects as Ransom:Win32/DriedSister.A!MTB.

  • SentinelOne 23.8+ (behavioral rule ID 84791) blocks “dried.exe” process creation even before encryption starts.

4. Other Critical Information

  • TTP in Brief:
    – Deletes local shadow copies (vssadmin delete shadows /all /quiet).
    – Creates hidden alternate data stream under C:\Recovery\recovery.dat:DriedLock:D (accessed for encryption key).
    – MITRE ATT&CK flow: T1566.001 (phishing attachment) → T1204.002 (malicious LNK) → T1055.012 (process hollowing) → T1486 (file encryption) → T1490 (inhibit recovery).

  • Broader Impact:
    – Disables Windows Update Service (wuauserv) to stop immediate security patching after encryption.
    – Drops fake malware dropper (Vidar stealer) packaged within ransom payment fake support chat sidebar; credentials collected are re-sold.
    – Initial targets were Japanese logistics and medical-device manufacturers, stretching to Canadian and European mid-tier distributors by December, leading Interpol to issue Purple Notice #2023-PN-392 on the operators.

Stay aware of jump-to-CN resolution commands (icedbucket[.]top, bucketred[.]biz) in ransom notes—those C2 servers rotate weekly.