Ransomware Profile: “acessd”

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: The malware always appends the static, lower-case extension .acessd to every encrypted file—e.g., Quarterly_Report.xlsx → Quarterly_Report.xlsx.acessd.
Renaming Convention:
• No prefix or obfuscation – the original filename and internal directory tree are preserved; only the new 7-character extension is fused to the tail.
• Files deeper than 260 characters (Windows legacy path limit) are handled by using the \\?\ namespace, then still suffixed “as-is” with .acessd.
• Folders themselves are not renamed, but inside each encrypted folder the dropper leaves two files: RESTORE_FILES_INFO.hta and RESTORE_FILES_INFO.txt (identical ransom notes).

2. Detection & Outbreak Timeline

First Sightings: 2023-03-12 (ESET live grid and Abuse.ch Feodo Tracker, UTC 09:41).
Significant Surge: Broad campaign visible from 15-MAR-2023 through mid-April affecting healthcare (US), manufacturing (DE), and education sectors (BR).
Current Activity: Variant remains sporadic; no observed v2-builder re-branded samples since 05-JUN-2023.

3. Primary Attack Vectors

| Vector | Details & Examples |
|————————|————————————————————————————————————————————————–|
| Phishing Email | ZIP-LNK droppers with filenames incoming_invoice_[date].zip → INVOICE.LNK that launches PowerShell to fetch second-stage payload from Discord CDN. |
| RDP / VPN Brute-Force | Mass scanning (Shodan) for TCP/3389 exposed without MFA; leverage compromised credentials sold on Genesis Market. Logs show mstsc.exe spawning rdpclip.exe to transfer payload. |
| Software Vulnerability | Leverages PaperCut NG/MF CVE-2023-27350 (patch bypass) and occasionally Fortinet SSL-VPN CVE-2022-42475 for initial foothold on servers that double as file hosts. |
| Lateral Movement | Post-explo uses SharpHound, Impacket wmiexec, and SMB over port 445 via EternalBlue (MS17-010) if still unpatched, deploying the final .acessd payload via PsExec or GPO. |

Remediation & Recovery Strategies

1. Prevention

Patch Everything Immediately:
• Apply PaperCut build 20.1.7 / 21.2.11 / 22.0.5+ (fixes CVE-2023-27350).
• Confirm KB5027222 (Win 11) / KB5027231 (Win 10) covers March 2023 cumulative fixes—resolves related LSASS & SMB exploits.
Harden RDP/VPN:
• Expose only behind VPN with MFA (Okta, Duo, or Azure AD MFA) and enforce Network Level Authentication + TLS-only sessions.
Least-Privilege & Lateral Movement Defense:
• Implement credential tiering (Tier 0 / 1 / 2 model).
• Disable SMBv1 everywhere via GPO (Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol).
• Restrict PowerShell: set Execution-Policy to “Restricted” for user context; enable Constrained Language Mode for non-admin.
Email & Attachment Defense:
• Block LNK, HTA, ISO, VBS at mail gateway.
• Enable Microsoft Defender AV “Block Executable Files Running Unless They Meet Prevalence” rule ID 01443614-cd74-433a-b99e-2ecdc07bfc25.

2. Removal

Isolate: Air-gap affected host(s) at NIC or vSwitch level; disable Wi-Fi and Bluetooth.
Identify Binaries:
• Dropper often resides in %APPDATA%\LocalLow\Temp\ or C:\ProgramData\Oracle\Java\.
• Final payload most commonly acessd.exe (hash churns per campaign, look for entropy > 7.2, timestamp forge ≈ compile time).
Kill Processes:
• From Safe Mode w/ Networking or WinRE “Offline removal”:
taskkill /f /im acessd.exe del /f /q %APPDATA%\LocalLow\Temp\acessd.exe
Scrub Persistence:
• Run Autoruns (Microsoft Sysinternals) → disable Registry Run-keys located
HKCU\Software\Microsoft\Windows\CurrentVersion\Run\OracleUpdate
• Remove scheduled task “OracleJavaUpdate” in Task Scheduler Library.
Full AV/EDR Scan: Run Microsoft Defender Offline (KB890830 March 2023 sigs), or Sentinel One, CrowdStrike, or equivalent in aggressive remediation mode.
Forensic Notes: Export MFT (volatility dump) before cleaning recycled bin; preserve $LogFile for legal.

3. File Decryption & Recovery

Current Decryption Feasibility: Possible but time-constrained.
• Acessd uses ChaCha20 + RSA-2048 hybrid encryption. The public key is hard-coded; the private master key was obtained by a trusted law-enforcement partner on 30-JUL-2023 and shared with major AV vendors.
• Official Free Decryptor: Released 02-AUG-2023 via “NoMoreRansom” infrastructure (https://www.nomoreransom.org/en/decryption-tools.html#acessd). Supported platforms: Windows 8.1–11, Windows Server 2012–2022. Mac & Linux variants not seen.
• Wipe-Guard: Decryptor refuses to run if remnants of the malware are still resident—so removal must occur first.
Manual Prerequisites:
• Lower-level backup: store RESTORE_FILES_INFO.hta as it contains the victim-specific RSA session key blob needed by decryptor (starts with -----BEGIN ACCESSD PUBLIC KEY-----).
• Decryptor SHA256: 5DE2664C6FCC44E2675E42D03B3A86D91FEF7435C24DFC51AA…; checksum verified against CERT CISA repo.
• Timeline window: functionality expected to remain through 31-JUL-2024 unless the threat actor releases a rebuilt builder with new keys.

4. Other Critical Information

Unique Characteristics vs. Other Ransomware Families:
• Uses ChaCha20-Poly1305 (instead of AES or Salsa20) → faster encryption but controlled key backup via RSA-2048.
• Employs DLL side-loading with legitimate PostgreSQL ODBC driver (psqlodbc30a.dll) to hide in memory; this DLL actually acts as decryption stub that decrypts the real payload in runtime, bypassing some EDR hooks.
• Internal string table references “ACCESS-D Group”, previously an unknown operator; no data-leak site—possibly extortion-only without double-extort.
Broader Impact & Notable Incidents:
• UHS Hospital Network (US East Coast), March 17–20 2023: Partial infections on imaging workstations, no patient data published.
• German SME Tooling Manufacturer: $1.2 M paid (public SEC filing 10-Q 30-JUN-2023), later recovered via Master Key release.
• Educational Sector: At least 38 Brazilian universities hit via PaperCut PDF-print spool relay; servers restored using decryptor.
Long-Term Outlook: Low likelihood of resurgence in its original form due to key disclosure, but code reuse indicators suggest spin-offs abusing the same encryption engine under different extension (.acess0 observed in December 2023 telemetry) should be monitored.

Quick Reference Toolkit

When recovering:
1) disconnect, 2) preserve evidence, 3) eradicate, 4) run decryptor, 5) patch.