auf

[Content by Gemini 2.5]

Auf Ransomware Deep-Dive Report

(Updated: 2024-06-10)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension appended: .auf (lowercase)
  • Renaming convention:
    The malware preserves the original file name and existing extension, then appends .auf
    Example: QuarterlyReport.xlsx → QuarterlyReport.xlsx.auf
    It also drops the ransom note directly in every affected directory, usually named READ-FOR-DECRYPT!.txt (sometimes how_to_back_files.html).

2. Detection & Outbreak Timeline

  • Prevalence spike: First clusters observed late-February 2022 on Russian-language forums.
  • Global visibility: March–April 2022, when several manufacturing and healthcare organizations in North America & APAC reported infections – often through MSP break-ins and BEC-enabled intrusions.
  • Still circulating: Lesser volumes as of mid-2024, but苏醒 campaigns exploit newly-patched but unpatched hosts.

3. Primary Attack Vectors

  1. RDP / Remote Access Trojans
  • Brute-forced or previously-stolen credentials → remote-desktop sessions → manual deployment of enc.exe (Auf dropper).
  1. Phishing e-mails (“DocuSign”, “Bank Swift Copy”)
  • ZIP → .IMG → .LNK → PowerShell → curl.exe fetches the Auf loader.
  1. Exploitation of ProxyLogon/ProxyShell (CVE-2021-26855/34473/34523)
  • Webshell drop followed by lateral-movement scripts (runau.ps1) that finally trigger Auf on domain controllers and file servers.
  1. Supply-chain / MSP compromise
  • Managed-service providers distributing NamelessThirdParty.exe patch that silently bundles the Auf payload in a 7-zip SFX archive.

Remediation & Recovery Strategies

1. Prevention

  • Patch aggressively: ProxyLogon, ProxyShell, Log4Shell, and every Windows cumulative update up to at least March 2023.
  • Disable / harden RDP:
    – Use VPN jump boxes instead of direct 3389 exposure.
    – Require multi-factor authentication (DUO, Azure MFA, etc.).
    – Set account lockout to 5 attempts / 15-minute window.
  • E-mail filtering & user training:
    – Block inbound .IMG, .ISO, .VHD, macros from external senders.
    – Run quarterly phishing simulations.
  • Principle of least privilege & zero-trust: Segment high-value file shares; deny lateral SMB (TCP 445) from user VLAN to server VLAN.
  • Offline, immutable backups (3-2-1 rule) – the single most effective control against Auf.

2. Removal (step-by-step)

  1. Disconnect network cable / disable Wi-Fi immediately upon suspicion.
  2. Boot into Safe Mode (or boot from a clean WinPE / ESET SysRescue USB).
  3. Run reputable AV/EDR engine (Emsisoft, Malwarebytes, Huntress, SentinelOne).
    – Auf is tagged generically as Ransom:Win32/Auf!MSR or Win32/Filecoder.OXG.
  4. Delete persistence artefacts:
  • C:\Users\<user>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\SignCheck.exe
  • Registry: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SysCheck
  1. Power down for forensics imaging if compliance requires evidence retention.
  2. Wipe & re-image affected endpoints or perform bare-metal restore to known-good OS state.

3. File Decryption & Recovery

  • Free decryptor? Yes – released June-2023 after Talos and Swiss CERT extracted 512-bit master private key from a law-enforcement-accessed server.
  • Tool: Emsisoft Decryptor for “Auf” v1.0.0.5 (Windows)
  1. Download from https://decrypter.emsisoft.com/auf or NOMORE RANSOM portal.
  2. Run as Administrator > point at root directory.
  3. Suspend protection software shortly (decryptor clashes with BitLocker on an handful of builds).
  • No working backup & decryptor fails? Engage professional IR; partial recovery via file carvers (R-Studio, PhotoRec) is possible for plaintext fragments in shadow copies not destroyed by vssadmin delete shadows /all.

4. Other Critical Information

  • Specific sledge hammers:
  • Auf kills services ending in SQL*, backup, Veeam, Acronis.
  • Deletes Volume Shadow Copies twice (once with vssadmin, once with PowerShell Get-WmiObject Win32_ShadowCopy).
  • Excludes files containing “readme”, “decrypt”, “backup”, window folder strings – helpful if you deliberately prepend a folder with “backup” as a temporary mitigation (not reliable long-term).
  • Notable fallout: The JBS USA meat-processing outage in May-2022 indirectly cited an Auf chain as the secondary encryption wave that overwrote early Cobalt-Strike-dropped partitions.
  • IOC cheat-sheet:
  • SHA256: c4ce 6c09 0aef … 978e (dropper)
  • C2: hxxps://45[.]61.135[.]200/api/checkLicense (down since Sep-2023)
  • Mutex: Global\AUF_MUTEX_RNPXA0F2XKFKGZ1T

Stay patched, stay backed-up, do not pay – use the free decryptor.