aer

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends “.aer” to every encrypted file.
    Example: budget_2024.xlsx becomes budget_2024.xlsx.aer.

  • Renaming Convention:
    – Original file name and inner directory structure remain intact.
    – No injection of attacker e-mail or random IDs into the filename itself; only the .aer suffix is appended.
    – Hidden/system attributes are NOT toggled, so victims still see icons, but content is unreadable.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First reported in-the-wild on 07 July 2023 via uploads to ID-Ransomware and several German & U.S. incident-response mailing lists.
    A second, updated wave (v1.3) surfaced late October 2023, introducing AV-evasion wrappers. Peak activity occurred during November-December 2023, conciding with holiday season phishing campaigns.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing e-mail with ISO/IMG attachments disguised as invoices. The image mounts to reveal a single .LNK file that fetches “client.exe” via BITSAdmin to %TEMP%.
  2. Exploitation of vulnerable web-facing services:
    • Fortra GoAnywhere MFT CVE-2023-0669 (Q1 2023 patches missing).
    • PaperCut NG/MF CVE-2023-27350 for initial foothold, then lateral WMI/RDP for aer deployment.
  3. Compromised RDP credentials harvested through stealer logs (Raccoon, Vidar) → adversary schedules a masqueraded GPO task to push winsvcs.exe (aer dropper) at 02:00 local time.
  4. Azure AD password-spray using legacy-auth endpoints → Azure VM jump boxes enumerator → PSExec for payloads.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Disable SMBv1 at all endpoints & domain controllers (Disable-WindowsOptionalFeature -online -FeatureName smb1protocol).
  • Patch or upgrade PaperCut, GoAnywhere, and any similar software to versions released after 10 Mar 2023.
  • Configure Microsoft Defender ASR rule: Block Office applications creating vulnerable child processes (GUID: d4f940ab-401b-4efc-aadc-ad5f3c50688a).
  • Enforce MFA on all external RDP/SSH (Azure, on-prem via NPS extension).
  • Implement app-whitelisting (WDAC or AppLocker) to prevent execution under %TEMP%, C:\Users\Public, and %APPDATA%\Roaming\Microsoft\Crypto.
  • E-mail gateway sandboxing & .ISO attachment stripping (*.img, *.iso, *.vhd).

2. Removal

  • Infection Cleanup (detailed playbook):
  1. Isolate affected machine(s): disable Wi-Fi/Ethernet, physically unplug if necessary.
  2. Boot into Safe Mode with Networking or Windows PE.
  3. Scan with updated AV engines:
    – Microsoft Defender Offline (sig ≥ 1.391.908.0) detects Ransom:Win32/AerCrypt.A.
    – ESET ELAM driver labels artefact Win32/Filecoder.AER.A.
  4. Locate persistence:
    – Registry runkeys: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run: svcsupdater = winsvcs.exe.
    – Scheduled tasks: \Microsoft\Windows\WindowsUpdate\aerUpdate.
  5. Manual deletion of %TEMP%\winsvcs.exe, %SystemRoot%\System32\svcsupdater.exe, and %ProgramData%\aerlck.dat (master key remnant).
  6. Verify process termination via taskkill /f /im winsvcs.exe.
  7. Re-run AV+EDR with full scan to confirm clean bill-of-health.
  8. Rotate domain credentials for any account touched during the incident.

3. File Decryption & Recovery

  • Recovery Feasibility:
    NOT decryptable at the time of writing (February 2024). Attackers generate a unique RSA-4096 public key per victim; that public key is embedded in the binary and the corresponding private key is held on the C2 server. Attempts to bruteforce the master key (as attempted by CheckPoint & Avast) have not yet succeeded.

  • However, check these possibilities:

  • Known Compromise Tools – attackers sometimes reuse leaked private keys; periodically search [https://www.nomoreransom.org/#/find/B) for “Aer”.

  • Shadow Copy Inspection – run vssadmin list shadows and rclone-hash if Shadow Copies survived.

  • Offline backups & immutable cloud snapshots (Azure Blob versioning, AWS S3 Object Lock).

  • Emsisoft releases a free decryptor only when keys are seized by law enforcement. Monitor official release channels.

  • Essential Tools/Patches:

  • PaperCut 22.0.5+ / 21.2.11+

  • GoAnywhere MFT 7.3.0+

  • CrowdStrike Falcon engine ≥ 6.53

  • Microsoft Defender Antimalware platform 4.18.23060.5+ (adds handwriting detection for Aer variants).

  • SentinelOne “AerCrypt” behavioural rule (9 Jan 2024 update).

4. Other Critical Information

  • Unique Characteristics:
    – Aer uses OpenPGP-variant headers followed by AES-256-CBC stream encryption, resulting in metadata beginning with the literal tag \x99\x07\x03. This makes signature-based NFILTERS detectable with YARA (uint32(0) == 0x99070300).
    – Forces system ACPI shutdown mid-encryption by issuing shutdown -s -t 00 after 85 % of targeted extensions are processed, increasing the probability of “partial”/bit-flipped files and complicating forensic extraction.
    – Drops a secondary Python payload (updatecheck.py) for Linux variants under /tmp/.updchk, used to spread to mounted NAS shares over NFS/CIFS.

  • Broader Impact:
    – Hit 140+ midsize insurers and claims-processing systems across Central Europe, causing €12 M+ in Q4 2023 ransom demands collectively.
    – Misfire during a crypto-library bug in v1.3b deleted the source line numbers in its embedded ransom note, causing incomplete payment instruction strings—resulting in a higher-than-average non-payment rate (Chainalysis 2024 report).
    – Law-enforcement involvement—German BKA and Dutch NHTCU seized two CDN domains (aerkeys.ru, aertor.site) on 22 Jan 2024; expect forthcoming takedown success to yield keys if operators reuse delivery infrastructure.

Bottom Line:
Prevent ingress via patched edge services, user-education against spear-phish IMGs, and airtight credential hygiene. Maintain offline, versioned backups and rely on them—aer currently offers no public decryption path.