asulo - NTAPINSIGHT

Asulo Ransomware Intelligence Sheet
File extension: “.asulo”

Technical Breakdown

| Section | Details |
|———|———|
| 1. File Extension & Renaming Patterns | – Extension appended: .asulo (lower-case).
– Renaming convention: [original_name][original_extension].id-XXXXXXX.[attacker_mail].asulo ‑ the id segment is a unique identifier for the victim, often 8 bytes in hex. |
| 2. Detection & Outbreak Timeline | – First sighting: 16 – 21 Jan 2024 (Eastern-European SOC feeds, independent uploads from South-East Asia).
– Peak propagation: End of Feb 2024 – mid-Mar 2024, coinciding with malvertising campaigns pushing cracked software & MSIX installers. |
| 3. Primary Attack Vectors | – Phishing/Malvertising: Rigged search-result ads for pirated utilities (Audacity “Pro”, Adobe-Patcher, KMS emulators).
– CVE-2023-36884 & CVE-2023-4863: Malicious DOCX with remote-template & WebP exploit in the same campaign kit.
– RDP / VNC brute-force: Initial foothold on exposed (TCP/3389, TCP/5900) Windows 10/11 workstations → PsExec lateral movement.
– Supply-chain poisoned MSI/MSIX: Digitally-evaded SmartScreen; installs Asulo dropper silently via msiexec. |

Remediation & Recovery Strategies

| Section | Actions & Resources |
|———|———————|
| 1. Prevention (pro-active) | 1. Patch CVE-2023-36884, CVE-2023-4863, CVE-2023-21768; switch to Chrome ≥117.
2. Disable legacy RDP and enforce Network-Level-Authentication + MFA via Windows Hello.
3. Group Policy to block execution from %USERPROFILE%\Downloads, %LocalAppData%\Temp, and %AppData%.
4. Enable Microsoft Defender ASR rules: “Block execution of potentially obfuscated scripts” & “Block Win32 API calls from macros”.
5. VSS secure-mode: vssadmin resize shadowstorage /for=C: /on=C: /maxsize=10% + implement immutable repositories (Azure Blob with “WORM”, Veeam Hardened Repo). |
| 2. Removal (infected host) | A. Air-gap from network immediately.
B. Clean-boot & offline scan:
– Windows 11 Installation Media → Troubleshoot → Command Prompt.
– diskpart san policy=offlineAll to prevent USB encryption bleed-through.
C. Delete persistence:
– Registry keys: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\AsuloSrv, HKLM...
– Scheduled tasks: AsuloUpdate, AsuloSys.
– Malwarebytes 4.6.x / ESET Online Scanner in safe mode removes the dropper and the watchdog DLL named asulo32.dll (x86) / asulo64.dll.
D. Reboot; confirm no active svhost.exe under %LocalAppData%\Asulo (note misspelling vs svchost). |
| 3. File Decryption & Recovery | – Current Status (May 2024): No free decryptor. Asulo uses Curve25519 + AES-256 in GCM mode with unique keys per victim; offline key only confirmed in January build, patched in February updates.
Restore options:
1. Check backup integrity first (Cloud-VSS, on-site disk snapshots).
2. Upload a pair (encrypted.jpg.asulo + original jpg) to NoMoreRansom.org check-tool regularly; if offline key is released, tool will output decryptable confirmation.
3. If no intact backup, identify stray VSS copies from before the attack with vssadmin list shadows and ShadowExplorer, mount and extract assets. |
| 4. Other Critical Information | – Unique Defensive Trigger: Creates mutex w0uf5y32–asulo–m0v3 across all user sessions; helpful for EDR retro-hunts (Event ID 1 Sysmon).
– Data Exfiltration: In approx. 29 % of observed infections the variant drops rclone.exe to upload sensitive folders to Cloudflare R2 buckets named “asulo-c2-xxxx”.
– Corporate Scope: Mapped drives via NTLM stolen to mount file shares; target intel like *\_finances\* or \SAP\Interface\.
– Insurance Note: Some policies now exclude Asulo if attributable to unlicensed software downloads—include this in breach response paperwork. |

Quick-Reference Toolkit

Bottom line: Isolate, patch aggressively, wipe the machine, restore only from verified backups, and monitor for the exfiltration vector.