Wild Neutron APT Sample Rule - file a14d31eb965ea8a37ebcc3b5635099f2ca08365646437c770212d534d504ff3c

Hunt Hypothesis

The detection identifies potential Wild Neutron APT activity through the execution of a suspicious file hash, indicating possible adversary persistence or data exfiltration. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage APT operations before significant damage occurs.

YARA Rule

rule WildNeutron_Sample_7 
{

    meta:
        description = "Wild Neutron APT Sample Rule - file a14d31eb965ea8a37ebcc3b5635099f2ca08365646437c770212d534d504ff3c"
        author = "Florian Roth"
        reference = "https://securelist.com/blog/research/71275/wild-neutron-economic-espionage-threat-actor-returns-with-new-tricks/"
        date = "2015-07-10"
        score = 60
        hash = "a14d31eb965ea8a37ebcc3b5635099f2ca08365646437c770212d534d504ff3c"

    strings:
        $s0 = "checking match for '%s' user %s host %s addr %s" fullword ascii /* PEStudio Blacklist: strings */ /* score: '24.00' */
        $s1 = "PEM_read_bio_PrivateKey failed" fullword ascii /* PEStudio Blacklist: strings */ /* score: '23.00' */
        $s2 = "usage: %s [-ehR] [-f log_facility] [-l log_level] [-u umask]" fullword ascii /* score: '23.00' */
        $s3 = "%s %s for %s%.100s from %.200s port %d%s" fullword ascii /* PEStudio Blacklist: strings */ /* score: '23.00' */
        $s4 = "clapi32.dll" fullword ascii /* score: '21.00' */
        $s5 = "Connection from %s port %d" fullword ascii /* PEStudio Blacklist: strings */ /* score: '17.00' */
        $s6 = "/usr/etc/ssh_known_hosts" fullword ascii /* PEStudio Blacklist: strings */ /* score: '16.00' */
        $s7 = "Version: %s - %s %s %s %s" fullword ascii /* score: '16.00' */
        $s8 = "[-] connect()" fullword ascii /* PEStudio Blacklist: strings */ /* score: '13.00' */
        $s9 = "/bin/sh /usr/etc/sshrc" fullword ascii /* score: '12.42' */
        $s10 = "kexecdhs.c" fullword ascii /* score: '12.00' */
        $s11 = "%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s" fullword ascii /* score: '11.00' */
    
    condition:
        uint16(0) == 0x5a4d and filesize < 5000KB and all of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 12 string patterns in its detection logic.

References

• https://securelist.com/blog/research/71275/wild-neutron-economic-espionage-threat-actor-returns-with-new-tricks/
• Source Rule

False Positive Guidance

• Scenario: Legitimate System Update via Windows Update
  Description: A file matching the hash is detected during a Windows Update process, which is a common method for deploying system patches.
  Filter/Exclusion: process.name == "wuauclt.exe" or process.parent.name == "svchost.exe"

• Scenario: Scheduled Job for Log Collection
  Description: A scheduled task runs a script that uses a file with the same hash as the rule, such as a log aggregation tool like logrotate or rsyslog.
  Filter/Exclusion: process.name == "logrotate", process.name == "rsyslog", or process.name == "syslog-ng"

• Scenario: Admin Task Using PowerShell for Configuration Management
  Description: An administrator uses PowerShell to configure system settings, and the script uses a file with the same hash as the rule.
  Filter/Exclusion: process.name == "powershell.exe" and user.name == "Administrator" or process.args contains "Configure-System"

• Scenario: Antivirus Quarantine File
  Description: A file with the same hash is detected as a quarantined file by an antivirus solution, which is then moved to a temporary directory.
  Filter/Exclusion: file.path contains "Quarantine" or file.path contains "Temp"

• Scenario: Legitimate Software Installation via MSI
  Description: A legitimate software package (e.g., Microsoft SQL Server) is being installed, and the installation process uses a file with the same hash.
  Filter/Exclusion: file.name contains "sqlservr.exe" or file.name contains "setup.exe" and process.name == "msiexec.exe"