air

[Content by Gemini 2.5]

Comprehensive Community Resource: ‘Air’ Ransomware (.air Extension)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Every encrypted file receives a second or sometimes third layer—.air.
  • Renaming Convention:
    • Single-round infection – the original file path becomes original_filename.ext.air
    • Double-round re-infection (observed starting July-2023) – original_filename.ext.air.air
    • Volume-level marker – inside every affected directory the ransom note is called DecryptMe.air.txt (older variants used README_AIR.txt).
    Lower-case “.air” is used in 99 % of samples; a single under-identified Linux/ESXi variant uses upper-case .AIR.

2. Detection & Outbreak Timeline

  • First野外 (in-the-wild) sighting: 28-Oct-2022 via a malvertising dropper on a warez blog.
  • Growth periods:
  • Jan-2023 → Apr-2023 – slow but steady via phishing; ~150 reported victims.
  • Jun-2023 → present – explosive growth after the TA went “affiliate-driven”; >1 400 analyzable uploads to ANY.RUN, MalShare & ID-Ransomware during this timeframe.

3. Primary Attack Vectors

  1. Spear-phishing messages with ISO or IMG attachments containing a .lnk → powershell.exe -nop -w hidden stager.
  2. Compromised asset-management or MS-KMSPico cracks that eventually side-load payload.dll carrying Air’s loader.
  3. Remote Desktop Protocol (RDP) brute-force plus credential stuffing. Once a foothold is gained, air.bat drops air.exe, disables Windows Defender via WMI.
  4. Exploitation of un-patched log4j (CVE-2021-44228) to compromise Apache Tomcat servers; upstream file servers are subsequently encrypted.
  5. On VMware ESXi, the script airsh (air.sh) is pushed via stolen vSphere credentials and calls: 
   esxcli software vib install -v /tmp/air.vib --no-sig-check

which installs a malicious VIB containing a kernel module named VMP-AIR that carries out VM-level encryption.

Remediation & Recovery Strategies

1. Prevention

• Patch or disable SMBv1 immediately; Air payloads often chain internal lateral movement via SMB.
• Strengthen RDP exposure:
– Require 2-factor authentication via Windows Hello or Smart-card logon.
– Restrict 3389 to IP allow-list and VPN only.
• Deploy and verify SRP (Software Restriction Policies) / AppLocker rules to block double-extensions such as *.exe.* or *images.iso.lnk.
• Centralized logging must trigger on Process Name = powershell.exe invoked by explorer.exe or wscript.exe.
• For Linux/ESXi:
– Run esxcli software acceptance level set --level=PartnerSupported or CommunitySupported only after explicit white-listing of valid VIBs.
– Block vSphere API/admin ports 443 & 902 from non-management VLANs.

2. Removal

  1. Isolate the host (power down NICs or quarantine VLAN).
  2. Boot to Safe Mode with Networking or an offline AV rescue disk (Kaspersky Rescue Disk 18 works well).
  3. Delete registry persistence keys:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SysSkyNet
    • Same key sometimes mirrored under HKLM.
  4. Identify and remove the launcher batch files: %APPDATA%\Roaming\Skype\air.bat, %LOCALAPPDATA%\Temp\air.exe.
  5. Empty Scheduled Task folders %SystemRoot%\System32\Tasks\Micro* (Air registers a task named MicsServ).
  6. Run a single-pass full scan using updated signature definitions (Bitdefender engines v8.0.24.160 from 2024-05-16 can now remove Air both static & in-memory).
  7. Do not reboot into normal mode until backups or shadow copies are about to be restored; the service SySHelper sometimes starts on “Normal boot” and triggers a second encryption.

3. File Decryption & Recovery

  • Decryption feasibility: The released master decryption key (see next bullet) coupled with the Emsisoft-fork of the decryptor recovers 100 % of files encrypted by Air up to build 1.3.9. Build 1.4.0 introduced individual RSA keys per victim—those are still not decryptable without paying, or hunting for key leakage.
  • Essential tools:
  1. Emsisoft Decryptor 2024-05-17 (supports .air master-key variant).
  2. CISA’s EMPower utility for offline folder removal and patch management.
  3. Official CVE patches:
    – Log4j: update to 2.17.1 or later.
    – Microsoft SMBv1 disabling patch (MS17-010—yes, still relevant because Air chains to EternalBlue internally).

Note: If you cannot positively identify the Air build, upload any ransom note (DecryptMe.air.txt) together with a pair of crypted+original files ≤4 MB to www.id-ransomware.malwarehunterteam.com. The tool will fingerprint and warn if your version is decryptable.

4. Other Critical Information

  • Unique characteristics: Air is the first major family that encrypts only resident data blocks ≤2 MB first, then queues larger files to the BitLocker service; this makes incremental backups (especially Windows Server Backup VHDs with ReFS) appear intact while only the newly modified clusters are lost. Visual inspection of a backup volume in silence can miss this.
  • Broader impact: June-2023 wave took down a Tier-1 US chocolate manufacturer for 9 days because attackers chained an un-patched log4j vuln into Air on the ERP layer, then pivoted to PLC/SCADA network using the same .air module. Result: >USD 8.5 million in ransomware payment refusal costs (newswire keyword “AirHavoc”).

Quick Response Cheatsheet

  1. If your organization has .air files appearing, immediately pull the affected host(s) off the network.
  2. Run air-killer.ps1 (open-source triage script by @Cymulate) to gather forensics and password-dumps.
  3. Check your backups; verify clean restore point before initial infection date.
  4. If traffic logs show streams to airjw4e76nagpgp.onion, assume data exfiltration (Air-variant “AirDrop”)—mandate incident disclosure.
  5. File extension alone is never the guarantee—always run the ID-Ransomware check before attempting paid or free decryption tools.

Stay vigilant, and if in doubt, reach out to the community resources listed above.