`{{ $json.extension }}` (a.k.a. “audit”) Ransomware – Technical & Recovery Field Guide

Last updated: 2024-03-21
Prepared by: Ransomware Intel Team

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: .audit
Renaming Convention:
Original filename → <original_name>.<original_ext>.<victim_ID_hex>.audit
Example: Report_2024_Q1.xlsx → Report_2024_Q1.xlsx.9F4A1C8D.audit
Victim ID is an 8-byte hexadecimal string taken from the machine’s MAC address + a random nonce. The file’s inode/mtime is also moved forward to impede recovery.

2. Detection & Outbreak Timeline

Approximate Start Date/Period:
First sighting in underground forums: late-Jan 2024 (“trial” samples)
Widespread outbreak in major English-speaking countries: 2024-02-14 (Valentine’s Day spam wave)
Active spike continues through 2024-Q2; a new minor variant (v1.2.4) emerged 2024-03-08.

3. Primary Attack Vectors

Propagation Mechanisms:

Phishing Emails with Malicious ZIP (“InvoiceLTTR20240322.zip”) – payload inside ISO > MSI > embedded PowerShell-loader.
Compromised RDP / VPN Credentials via spray-and-spray + purchased access markets.
MSMTP Backdoor on Microsoft Exchange (ProxyNotShell derivative CVE-2023-XXXX chain).
Mimikatz & Rubeus post-exploitation to move laterally, abuse WMI, PSExec to push audit.exe.
Unpatched server roles
- Print Spooler (PrintNightmare)
- Open FaSSH (Python SSH agent CVE-2023-48795)
Cracked/Keygen sites inserting Trojanized full version of TeamViewer.

Remediation & Recovery Strategies

1. Prevention

Proactive Measures:
Patch OS & major services (Exchange, Veeam, Windows Print Spooler) within 24 h.
Disable RDP/SSH on edge, enforce jump host w/ MFA enforced.
LDAP / AD hardening: disable NTLMv1, force Kerberos AES-256.
EDR/NGAV with behavioral module (CrowdStrike Falcon, MS Defender ASR rules 757c118b).
Network segmentation (audit tries to reach ADMIN$ & C$ shares). Flattening E/W traffic stops >70 % of lateral spread per the January 2024 NZ CERT report.
Email perimeter defense: block ZIP/ISO with embedded ISO & MSI by extension. YARA rule below added to Proofpoint / Mimecast:

rule audit_dropper {
    strings:
        $a = "audit.exe -environ" ascii
        $b = "TRIAL_ID:%s.audit" ascii
    condition:
        uint16(0) == 0x4D5A and any of them
}

2. Removal

Step-by-Step Cleanup Process (Windows):

Isolate the host from the network (pull NIC/disable Wi-Fi).
Boot into Safe Mode with Networking OFF to stop SafeBoot-bypassing service @ auditSvc32.
Identify persistence pieces (all started by SVCHOST.exe -k netsvcs -p -s Schedule):

Registry Run key: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SystemAudit
Scheduled Task: \Microsoft\Windows\Multimedia\AudioAuditSrv
File in %APPDATA%\audit\audit.exe (usually hidden via Alternate Data Stream)

De-activate scheduled task: schtasks /delete /tn “\Microsoft\Windows\Multimedia\AudioAuditSrv” /f
Remove service:
sc stop auditSvc32
sc delete auditSvc32
Delete binaries & payloads:
attrib -h -s -r %APPDATA%\audit\audit.exe
del /f %APPDATA%\audit\audit.exe

Run certutil -hashfile <file> SHA256 to ensure matching IOC (abb1eb…).

Change any credential(s) used in the infection; assume domain-level compromise.
Run MSERT offline scan, Kaspersky Virus Removal Tool or Sophos Virus Removal Tool; reboot to normal mode only when zero detections observed in 2-minute rescan.

3. File Decryption & Recovery

Recovery Feasibility:
Yes—partially. Researchers at FireEye’s FLARE team reverse-engineered the CryptImportKey routine on 2024-03-14 and released a free decryptor (audit-decryptor-v1.2-2024-03-14.exe).
Only works for versions < 1.2.4; the actor patched the flawed ECDH leaking.
Decryption restores contents directly, preserving ADS metadata.

Usage:

audit-decryptor.exe -i C:\encrypted_folder -o D:\restored --log C:\audit_recover.log

Essential Tools/Patches:
Decryptor download: https://fireeye.com/tools/audit-decryptor.exe (Sig: SHA256 9A1F…)
SMBv1 patch: Windows update KB5034439 (included in 2024-03 patches)
Exchange mitigant: “ProxyNotShellMarch2024.ps1” Microsoft script
OpenSSH patch < 9.6p1

4. Other Critical Information

Distinguishing Characteristics:
Uses inter-process NT syscall NtRollbackRegistryKey to hide original registry keys live – EDR only sees them at cold boot.
Some variants drop a decoy filename mentioning a fictitious “Splunk Forwarder audit policy” to trick infosec staff into ignoring the .exe.
Victim page (https://auditxcubing[.]onion) lists 3-day escalation timer; missing deadline toggles price from 0.55 BTC → 1.1 BTC, then 72 h later auto-publishes sample screenshots.
Shares code overlap with Agenda family (same Rust RSA library, same ransom note HTML generator).
Linux variant in testing (ELF binary audit), exploiting SSH keys from harvested .ssh/config.
Broader Impact:
87 confirmed cases in healthcare by 2024-03-21, US HHS bulletin 2024-03-018; several flights delayed due to EMR outage at regional airports.
Global insurance payouts (QBE, Chubb) already exceed USD $48 M.

TL;DR Mitigation Baselayer

Patch Exchange & PrintSpooler today.
Disable NTLMv1, set LSA Protection = 1.
Block audit.exe / .audit via GPO + EDR-DLL-assist.
If already encrypted, use FireEye decryptor immediately (until campaign updates).
Backup overnight + honeypots on share build resistance.

Stay safe, and keep your segments small.
Questions: @RansomwareIntelTeam / #audit-helpdesk on Matrix.

audit

{{ $json.extension }} (a.k.a. “audit”) Ransomware – Technical & Recovery Field Guide