apt nix elf derusbi

Hunt Hypothesis

The hypothesis is that the detection rule identifies potential malicious ELF files associated with the Derusbi APT, which may indicate initial compromise or lateral movement within a network. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage APT activity before it leads to data exfiltration or system compromise.

YARA Rule

rule apt_nix_elf_derusbi
{

    meta:
        Author = "@seifreed"

    strings:
        $ = "LxMain"
        $ = "execve"
        $ = "kill"
        $ = "cp -a %s %s"
        $ = "%s &"
        $ = "dbus-daemon"
        $ = "--noprofile"
        $ = "--norc"
        $ = "TERM=vt100"
        $ = "/proc/%u/cmdline"
        $ = "loadso"
        $ = "/proc/self/exe"
        $ = "Proxy-Connection: Keep-Alive"
        $ = "Connection: Keep-Alive"
        $ = "CONNECT %s"
        $ = "HOST: %s:%d"
        $ = "User-Agent: Mozilla/4.0"
        $ = "Proxy-Authorization: Basic %s"
        $ = "Server: Apache"
        $ = "Proxy-Authenticate"
        $ = "gettimeofday"
        $ = "pthread_create"
        $ = "pthread_join"
        $ = "pthread_mutex_init"
        $ = "pthread_mutex_destroy"
        $ = "pthread_mutex_lock"
        $ = "getsockopt"
        $ = "socket"
        $ = "setsockopt"
        $ = "select"
        $ = "bind"
        $ = "shutdown"
        $ = "listen"
        $ = "opendir"
        $ = "readdir"
        $ = "closedir"
        $ = "rename"

    condition:
        (uint32(0) == 0x4464c457f) 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
• Source Rule

False Positive Guidance

• Scenario: A system administrator is using binwalk to analyze a firmware image for embedded device analysis.
  Filter/Exclusion: Exclude processes where the command line includes binwalk or firmware in the argument.

• Scenario: A scheduled job runs strace to monitor system calls for debugging a custom application.
  Filter/Exclusion: Exclude processes where the command line includes strace or --trace and the parent process is a known debugging tool.

• Scenario: A developer is using objdump to analyze a compiled binary for reverse engineering purposes.
  Filter/Exclusion: Exclude processes where the command line includes objdump or --source and the user is a developer with known reverse engineering tools.

• Scenario: A security team is running a YARA scan on a sandboxed environment to test for known malware signatures.
  Filter/Exclusion: Exclude processes where the command line includes yara or --file and the process is running in a known sandbox or analysis environment.

• Scenario: A DevOps engineer is using gdb to debug a service that was recently deployed.
  Filter/Exclusion: Exclude processes where the command line includes gdb or --examine and the parent process is a known service or application.