aes_ni_0day - NTAPINSIGHT

Technical Breakdown:

Confirmation of File Extension: .aes_ni_0day (the string is appended as a secondary extension: original.ext.aes_ni_0day).
Renaming Convention: AES-NI renames files by retaining their original name and first extension, then simply concatenating .aes_ni_0day.
Example:
Quarterly-Report-Q2.xlsx → Quarterly-Report-Q2.xlsx.aes_ni_0day
Directories and network shares are processed recursively; files that are locked by other processes are skipped and queued for later encryption once they are released.

Approximate Start Date/Period: The first large-scale sightings of AES-NI (the “0day” campaign) were reported between December 2016 – January 2017, bearing strong similarities to the earlier AES-NI strain that appeared in late 2016. Rapid expansion was seen again in late 2020/early 2021 when threat-actors rebranded the locker and pushed it to high-value RDP-exposed targets.

RDP Compromise: Brute-force, credential-stuffing, or purchase of valid credentials on dark-web markets.
Unpatched SMBv1 / EternalBlue: Although SMBv1 has been deprecated since 2017, legacy or unpatched 2008-R2 / 2012 hosts continue to fall.
Phishing & Malicious Attachments: ZIPs containing JScript droppers or Office documents with macro-based boot-strappers.
Software Supply-Chain Backdooring: Notable in 2021 the attackers piggy-backed on a legitimate MSP/GPO script repository, which then spawned AES-NI binaries into client environments en masse.
Post-exploitation Lateral Movement: Uses PSExec, WMIC, and PowerShell remoting once a domain credential is captured.

Proactive Measures:
• Disable and remove SMBv1 on every Windows host (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
• Enforce strong, unique RDP credentials + rate-limiting (e.g., only VPN access, block tcp/3389 from the Internet).
• Enable multi-factor authentication for any external-facing admin service (VPN, RDP Gateway, VDI).
• Patch against stolen NSA exploits (MS17-010 for EternalBlue, plus newer CVE-2020-1472 Zerologon).
• Segment networks—use VLANs or firewalls so a single workstation breach cannot broadcast laterally.
• Run endpoint detection & response (EDR) in “block” mode and disable macro execution from the Internet zone.

Isolate: Disable NIC or pull power from affected host; place on a separate, firewalled VLAN.
Identify Privilege Escalation: Run Process Explorer / EDR console to spot unusually-named service executables (*.exe in %APPDATA%, sysWOW64, C:\Windows\Temp\ or C:\Intel\{GUID}\).
Kill Process Tree: Shut down the AES-NI binary and any vssadmin delete shadows child processes (older builds call bcdedit /deletevalue recoveryenabled to block Safe-Mode).
Delete Scheduled Tasks & Autoruns:
– Query schtasks /query /fo list /v and delete entries named “System Network Service Check” or similarly misleading names.
– In Registry: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run, RunOnce, and RunServices keys.
Undo Registry Permissions: AES-NI often sets restrictive ACLs on HKLM\SYSTEM\CurrentControlSet\Services to prevent automated removal; restore defaults via regini or icacls.
Scan with Updated AV & EDR: Ensure the daily sig-set version is later than the sample. Several engines detect under aliases: Trojan-Ransom.Win32.Acn/AES-NI, Ransom:Win32/AES-NI, Ransom:MSIL/AgentTesla.
Forensic Imaging: Prior to re-imaging, image disk(s) for possible evidence or future offline decryption efforts.

Recovery Feasibility:
• Secure Decryptor Exists — YES. There are two public, working decryptors for AES-NI strains:
1. AES-NI Decryptor v2.1 (Kaspersky Security Network) – released April 2017, updated July 2021.
2. Rakhni Decryptor (Trend Micro Rescue Disk) – broadly compatible, checks for the .aes_ni_0day header and extracts the 2048-bit RSA-wrapped AES key.
  • Prerequisites: The tool requires either:
  – An intact, original file + an encrypted pair (same content), OR
  – All 256 byte RSA-encrypted key blocks („rec.hta“ note often contains the block offsets) if malware crashed mid-run.
  • Usage: Do NOT pay. Run the decryptor as Administrator with simulated write test (-check-only switch) first, then execute actual decrypt.
  • Shadow Copies & Backups: If shadow-copy deletion failed (vssadmin delete shadows /all /quiet), use ShadowExplorer or native vssadmin list shadows to recover previous restore points. Always restore from offline backups before decryptor to avoid hashing collisions.

Additional Precautions:
• AES-NI has an optional data exfiltration module; search for large egress transfers (TLS/443 to domains ending *.center, *.top). Assume data is leaked—breach notification should follow.
• Logs: Malware writes its working directory path to %TMP%\query.txt; attackers also post latest.log to determine which workstations were skipped. Harvest these artifacts for IOC correlation.
• Crypto-evolution: Some late-2021 AES-NI forks remove .aes_ni_0day entirely and adopt .AES256, so verify headers (AES-EncryptXXXXXX) rather than rely solely on extension.
Broader Impact:
• Targeted both enterprise IT and critical manufacturing. Germany, Ukraine, and US healthcare chains reported $25 M in lost production during late-2020 wave.
• Helped pivot awareness toward mandatory MFA on RDP and eventual finalization of the SMBv1 deprecation roadmap in mid-2023.

Stay vigilant, keep cold/offline backups, and never rely on a single vector of defense.