Defending EDR Against Adversaries

Summary

The article examines how attackers use Bring Your Own Vulnerable Driver techniques to obtain kernel-level access and disable or remove endpoint protection tools such as antivirus and EDR platforms. It outlines several common tactics, including abuse of firewall rules, misuse of signed but vulnerable drivers, and reliance on remote access tools to maintain persistence while weakening security visibility. Real-world cases show how stolen VPN credentials, malicious advertising, and legitimate drivers with known flaws can be used to terminate security processes. The central concern is the rising threat of kernel-level attacks that create a blind spot where adversaries can operate with reduced detection.

Investigation

Huntress documented incidents in early 2026 in which attackers used stolen SonicWall VPN credentials to deploy a custom EDR-killer binary that abused a revoked EnCase forensic driver. In a later case, a malicious ad led to installation of ScreenConnect, after which a vulnerable Huawei audio driver was used to terminate security services. Across these investigations, Huntress observed repeated driver abuse, process-killing loops, and the use of trusted signed drivers to evade basic static detection.

Mitigation

Recommended defenses include detecting real-time abuse of vulnerable drivers, monitoring for unexpected firewall rule changes, and enforcing strict controls around driver signing and loading. Huntress also introduced detections for TrueSight driver abuse and automated cleanup of malicious firewall rules. Additional protection can come from tamper-protection features and tighter control over exclusions to make it harder for attackers to stop or uninstall EDR tools.

Response

If this activity is detected, isolate the affected system immediately, reverse any unauthorized firewall changes, unload or block the malicious driver, and reinstall or repair impacted EDR or antivirus agents. Security teams should then perform forensic analysis to uncover any added persistence mechanisms or stolen credentials and rotate privileged accounts such as VPN credentials.

Simulation Execution

Prerequisite: The Telemetry & Baseline Pre‑flight Check must have passed.

Attack Narrative & Commands

The adversary aims to disable the organization’s EDR telemetry by inserting a firewall rule that blocks all outbound traffic to known EDR cloud endpoints. To increase the chance of detection, the rule name explicitly mentions “EDR”. The steps are:

1. Enumerate known EDR endpoints (hard‑coded for demo).
2. Create a blocking outbound rule named “Block EDR Communications”.
3. Verify that the rule is active and that outbound traffic to the EDR domains is dropped.
4. Observe the generation of EventID 2004 with the malicious rule name, which should trigger the Sigma rule.

Regression Test Script

# -------------------------------------------------
# Simulation Script – Create Malicious Firewall Rule
# -------------------------------------------------
# 1. Define EDR endpoint list (example)
$edrEndpoints = @("edr.contoso.com","logs.edr.contoso.net")

# 2. Create a blocking outbound rule for each endpoint
foreach ($host in $edrEndpoints) {
    $ruleName = "Block EDR Communications - $host"
    New-NetFirewallRule `
        -DisplayName $ruleName `
        -Direction Outbound `
        -RemoteAddress $host `
        -Action Block `
        -Profile Any `
        -Enabled True `
        -Protocol Any
    Write-Host "Created rule: $ruleName"
}

# 3. Output the list of newly created rules for verification
Get-NetFirewallRule -DisplayName "*Block EDR Communications*"

Cleanup Commands

# -------------------------------------------------
# Cleanup Script – Remove Malicious Firewall Rules
# -------------------------------------------------
Get-NetFirewallRule -DisplayName "*Block EDR Communications*" | Remove-NetFirewallRule -Confirm:$false
Write-Host "All malicious EDR blocking rules removed."