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Introduction:
Cybersecurity researchers have exposed SSHStalker, a novel botnet that weaponizes the legacy Internet Relay Chat (IRC) protocol to command and control infected hosts. By masquerading as benign encrypted IRC traffic, SSHStalker evades modern EDR and NDR solutions that rarely scrutinize this decades‑old protocol. It compromises exposed SSH servers via credential brute‑force, then deploys a modular, Go‑based agent capable of log tampering, anti‑debugging, and plugin‑based payload execution. This marks a strategic pivot from noisy ransomware drops to quiet, persistent footholds inside critical infrastructure.
Learning Objectives:
- Analyze how SSHStalker abuses legitimate IRC encryption to hide C2 traffic in plain sight.
- Perform host‑based and network‑based detection of legacy‑protocol abuse and SSH brute‑force artifacts.
- Harden SSH configurations and implement behavioural monitoring to counter low‑and‑slow intrusions.
You Should Know:
- Detecting IRC‑Based C2 Traffic on Linux and Windows
SSHStalker uses IRC over TLS (IRCS) on non‑standard ports (e.g., 6697, 9999) or even common web ports. Because IRC is rarely allowed in corporate environments, its presence is often malicious.
Step‑by‑step guide for network defenders:
Linux (Zeek + tshark):
Capture IRC commands even on non-standard ports sudo tshark -i eth0 -Y "irc.command == NICK or irc.command == USER or irc.command == JOIN or irc.command == PRIVMSG" -T fields -e ip.src -e ip.dst -e irc.command -e irc.request Zeek script to log all IRC activity regardless of port (local.zeek) @load protocols/irc/main redef restrict_irc_ports = vector(); Removes port restriction
Windows (PowerShell + NetMon):
Find connections to common IRC ports
Get-NetTCPConnection | Where-Object {$_.RemotePort -in 6667,6697,9999,7000} | Format-Table LocalAddress,RemoteAddress,State,OwningProcess
Use Wireshark command line (tshark.exe) similarly
.\tshark.exe -r capture.pcap -Y "irc"
2. Analysing SSHStalker’s Go Binary for Anti‑Debugging
The botnet is compiled with Go, stripped of debug symbols, and employs `ptrace(PTRACE_TRACEME)` to prevent debugging and `runtime.LockOSThread()` to hinder sandboxing.
Linux static analysis:
Identify Go binaries file sshstalker.bin Shows "ELF 64-bit LSB executable, Go BuildID" strings sshstalker.bin | grep -i "ptrace|gdb|debug" Use radare2 to find anti-debug syscalls r2 -A sshstalker.bin [bash]> axt sym.ptrace Cross-reference ptrace usage [bash]> pdf @ sym.ptrace Disassemble
Windows analysis (IDA Pro Free / x64dbg):
- Set breakpoint on `NtSetInformationProcess` to detect `ProcessDebugFlags` manipulation.
- Check for `IsDebuggerPresent` and `CheckRemoteDebuggerPresent` calls.
3. Investigating SSH Brute‑Force and Persistence Artifacts
SSHStalker scans for SSH servers on port 22, then uses a hard‑coded wordlist. Once access is gained, it downloads the main payload and installs an SSH public key for persistence.
Linux forensics:
Check authorized_keys for unusual entries
cat ~/.ssh/authorized_keys
ls -la /home//.ssh/authorized_keys /root/.ssh/authorized_keys
Review SSH authentication logs for brute-force patterns
grep "Failed password" /var/log/auth.log | awk '{print $1,$2,$3,$11}' | sort | uniq -c | sort -nr
grep "Accepted" /var/log/auth.log | grep -v "sudo"
Detect recently modified SSH configuration files
find /etc/ssh -name "sshd_config" -mtime -7 -exec ls -la {} \;
Windows (if SSH server present via OpenSSH):
Check Windows OpenSSH authorized_keys
Get-Content "C:\ProgramData\ssh\administrators_authorized_keys"
Review Event ID 4625 (logon failure) for brute-force
Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4625} -MaxEvents 1000 | Where-Object {$_.Properties[bash].Value -like 'ssh'}
- Tampered System Logs: Recovering `utmp` / `wtmp` / `lastlog`
SSHStalker clears or zeroes out login records to erase its tracks. These logs can often be partially recovered from core dumps or memory.
Linux recovery attempts:
Check if wtmp file was truncated file /var/log/wtmp Compare file size with typical sizes stat /var/log/wtmp Use tct (The Coroner's Toolkit) tools Recover deleted wtmp entries if filesystem hasn't been heavily written sudo foremost -t log -i /dev/sda1 -o /recovery/lastlog Manual inspection of raw wtmp with utmpdump utmpdump /var/log/wtmp.bak If backup exists
Windows (PowerShell):
Event logs rarely zeroed easily; check for Event ID 1102 (audit log cleared)
Get-WinEvent -LogName System | Where-Object {$_.Id -eq 104} Log clearing event
5. Configuring SSH Hardening Against Credential Theft
The single biggest infection vector remains weak SSH credentials.
Linux server hardening (one‑liner):
Disable password authentication entirely sudo sed -i 's/^PasswordAuthentication yes/PasswordAuthentication no/' /etc/ssh/sshd_config && sudo sed -i 's/^PasswordAuthentication yes/PasswordAuthentication no/' /etc/ssh/sshd_config && sudo systemctl restart sshd Enable key-only authentication and set strict modes echo "PubkeyAuthentication yes" | sudo tee -a /etc/ssh/sshd_config echo "StrictModes yes" | sudo tee -a /etc/ssh/sshd_config
Windows OpenSSH hardening:
Disable password auth in Windows OpenSSH Set-ItemProperty -Path "HKLM:\SOFTWARE\OpenSSH" -Name DefaultShell -Value "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" Edit sshd_config: set PasswordAuthentication no Add-Content -Path "C:\ProgramData\ssh\sshd_config" -Value "PasswordAuthentication no" Restart-Service sshd
6. Simulating SSHStalker‑Style IRC C2 for Detection Testing
To validate your monitoring stack, set up a benign IRC server and generate similar traffic.
Linux (ngIRCd + socat):
Install minimal IRC daemon sudo apt install ngircd Configure to listen on SSL (self-signed cert) sudo ngircd -n -f /etc/ngircd/ngircd.conf Simulate bot JOIN/PART commands socat - OPENSSL:localhost:6697,verify=0 <<EOF NICK stalker_test USER test 0 :test JOIN c2 PRIVMSG c2 :heartbeat QUIT EOF
Windows (InspIRCd + HexChat scripting):
– Install InspIRCd, configure SSL.
– Use HexChat with Python scripting to auto‑join channels and send periodic messages.
7. API Security and Cloud Hardening Relevance
If SSHStalker later deploys plugins targeting cloud metadata APIs (a likely evolution), defenders must lock down instance metadata access.
AWS metadata service hardening (IMDSv2 required):
Require IMDSv2 on existing EC2 instances aws ec2 modify-instance-metadata-options --instance-id i-123 --http-tokens required --http-endpoint enabled Block access via iptables (defence in depth) sudo iptables -A OUTPUT -d 169.254.169.254 -p tcp --dport 80 -m owner --uid-owner root -j ACCEPT sudo iptables -A OUTPUT -d 169.254.169.254 -p tcp --dport 80 -j DROP
Azure IMDS hardening:
Disable IMDS on VM (if not needed) az vm update --resource-group myGroup --name myVM --set 'properties.networkProfile.networkInterfaceConfigurations[bash].properties.privateIpAddressConfigurations[bash].properties.privateIpAddressVersion=IPv4'
What Undercode Say:
- Key Takeaway 1: Attackers are weaponising legacy, trusted protocols (IRC) specifically because modern SOCs no longer baseline them. IRC traffic today is almost exclusively malicious.
- Key Takeaway 2: SSH misconfiguration remains the easiest entry point. Password authentication should be eliminated entirely, not merely discouraged. Combined with plugin‑based payloads, SSHStalker shows that initial access is now merely a foothold for deeper, modular exploitation.
- Analysis: SSHStalker is not a sophisticated zero‑day exploit—it succeeds because fundamentals are ignored. While the industry chases AI‑driven attacks, adversaries quietly abuse plaintext credentials and 30‑year‑old protocols. The shift to Go binaries is significant: cross‑platform, hard to statically analyse, and easy to obfuscate. Defenders must therefore pivot to behaviour‑based detection (e.g., unusual SSH key writes, long‑lived IRC connections) rather than signature matching. The modular plugin architecture means DDoS or data theft modules can be swapped in overnight; the initial intrusion is only the beginning.
Prediction:
The SSHStalker botnet foreshadows a wave of legacy‑protocol re‑emergence—expect copycat groups to weaponise Finger, RSH, or even Gopher protocols within the next six months. As Go and Rust become the default for malware authors, defenders will face a deluge of unique, hard‑to‑reverse binaries. The next iteration of SSHStalker will likely incorporate WebSocket‑based C2 fallback channels to bypass corporate IRC blocks entirely, and will use compromised SSH keys to pivot laterally into cloud DevOps pipelines, targeting Kubernetes clusters and CI/CD secrets.
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IT/Security Reporter URL:
Reported By: Omar Eldeeb – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
