🕷️ ShadowStrike: The Rise of a New OpenSSH Bruteforce Botnet Targeting Linux ServersAuthor: CyberDudeBivashPublished: July 31, 2025Source Intelligence: GreyNoise, SANS ISC, CyberDude Threat Lab

📌 Executive Summary

A new botnet dubbed “ShadowStrike” is actively targeting public-facing Linux servers with weak or default SSH credentials. Using brute-force techniques, it compromises exposed systems and weaponizes them to spread laterally across networks.

This botnet is engineered in Go (Golang) with advanced features like anti-VM evasion, real-time command-and-control (C2) switching, and port-scanning propagation.The rise of ShadowStrike highlights the critical importance of SSH hardening, credential hygiene, and behavioral detection in cloud and server environments.

🧠 Technical Analysis

🎯 Attack Vector

• Initial Access: Brute-force SSH on port 22/tcp
• Target: Linux-based servers (Debian, Ubuntu, CentOS, Alpine)
• Authentication Bypass: Exploits weak SSH login credentials via credential stuffing and known leaked combos

⚙️ Botnet Capabilities

🔬 Golang Loader Breakdown

• Language: Golang binary, statically compiled
• Architecture: Targets x86_64 and ARM devices
• C2 Communication: Uses base64+AES encrypted payloads over HTTP POST
• Obfuscation: Function names stripped, binary bloated with junk strings to bypass static AV
• Sample Hash (SHA256):

  wasmb21c91c0a98ef2d1e0f76f4293a234efb2831f32b46b7d648e2d199db7b0287c

🌐 Threat Infrastructure

• Active C2 Domains:
  • dns-shadow[.]xyz
  • cdn-scan[.]onion
• Hosting: FastFlux botnet infra with exit nodes in Russia, Ukraine, Brazil
• Toolkits Detected: Integration with Masscan, Hydra, SSHpass

🔍 Indicators of Compromise (IOCs)

🛡️ Mitigation & Hardening Guide

✅ Immediate Actions

• Block IPs identified from threat feeds and GreyNoise telemetry
• Kill active sessions from suspicious geolocations
• Isolate infected endpoints from internal networks

🔐 Hardening SSH Config

bash# /etc/ssh/sshd_config recommendations
PermitRootLogin no
PasswordAuthentication no
ChallengeResponseAuthentication no
AllowUsers youradmin
Port 2222

🔒 Use Key-Based Authentication

bash# Generate and copy SSH keys
ssh-keygen -t ed25519
ssh-copy-id user@your-server

📈 Monitoring & Detection

• Enable and monitor logs: /var/log/auth.log or /var/log/secure
• Use fail2ban or CrowdSec to ban brute-force attempts
• Watch for unusual outbound connections or HTTP POST to unknown hosts

📡 YARA Rule Snippet (Sample)

yararule ShadowStrike_Loader
{
    meta:
        description = "Detects ShadowStrike Golang-based botnet loader"
    strings:
        $golang = "Go build ID"
        $aes = "aes.NewCipher"
        $cmd1 = "/bin/bash"
    condition:
        uint16(0) == 0x7f45 and all of them
}

🔍 Attribution Possibilities

• Infrastructure Overlap: Some C2s previously linked to "Kaiji" botnet
• Language & Build Pattern: Suggests Eastern European developer background
• Motivations: Currently unclear; could evolve into ransomware or cryptojacking

🧩 Strategic Recommendations for Organizations

• Conduct an external perimeter audit for exposed SSH servers.
• Enforce MFA for SSH via tools like Duo or Google PAM.
• Integrate honeypots to detect ShadowStrike scanning activity (e.g., Cowrie, T-Pot).
• Review firewall settings to geo-block regions not relevant to operations.
• Automate alerts for new SSH logins from unknown public IPs.

📌 Conclusion

ShadowStrike exemplifies the modern evolution of SSH-targeting botnets — combining speed, anti-analysis, and modular C2 infrastructure to maximize infection rates.The use of Golang, DNS-based C2 switching, and stealth techniques make it a serious threat for DevOps teams, cloud service providers, and exposed Linux infrastructure.

⚠️ If you operate Linux servers with public IPs, now is the time to audit your SSH access policies and update your defenses.

CyberDudeBivash will continue tracking the evolution of ShadowStrike and similar botnets — stay tuned for IOCs, malware reports, and real-time threat feeds.

🧠 Authored by

CyberDudeBivash Threat Intel Division

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