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    EDR‑Freeze: How a User‑Mode WER Trick Can Put Security Agents on Ice and What Defenders Can Do

    By Ran Dubin - CTO

    Tags: prevention, zero-trust, EDR Bypass, EDR-FREEZE

    Published: October 20, 2025

    A new proof‑of‑concept technique dubbed EDR‑Freeze demonstrates how adversaries can exploit Windows Error Reporting (WER) to suspend endpoint protection agents directly
    from user mode without relying on vulnerable drivers or kernel exploits. This capability effectively places security sensors “on ice,” creating a temporary blind spot that attackers can
    leverage for privilege escalation or persistence.

    Although the approach appears novel, defenders have several effective mitigations available today.  By monitoring WER activity targeting sensitive process IDs, alerting on anomalous WerFaultSecure.exe executions, and enforcing least‑privilege policies, organizations can significantly reduce exposure.  Combined with zero-trust isolation technologies, these controls
    ensure that even when detection is momentarily disrupted, prevention remains intact.

    This post explains the EDR-Freeze technique in accessible terms, explores its implementations for enterprise defense, and maps it to practical mitigations that can be implemented immediately.

    Background – How EDRs Work and Why They are Target

    Endpoint Detection and Response (EDR) solutions form the frontline of modern enterprise defense. Their purpose is twofold: to detect malicious activity occurring on endpoints in real
    time and to respond to those events through containment, remediation, and forensics.

    An EDR agent typically consists of two core components:

    1. Kernel-mode drivers that monitor low-level system operations such as process creation, file access, memory injection, and registry changes.
    2. User-mode services that collect telemetry, apply behavioral analytics, and communicate findings back to a central management console or cloud backend.

    Together, these components give security teams visibility into suspicious behaviors like credential theft, lateral movement, and exploitation of legitimate system tools (so-called living-off-
    the-land binaries
    , or LOLBins).

    In most enterprises, EDRs have become the default trust anchor on endpoints. Incident responders rely on their continuous visibility to detect intrusions early, and security operations
    depend on them for automated correlation and triage.

    Why Attackers Target EDRs

    From an adversary perspective, the EDR agent is both an obstacle and an opportunity. Once malicious code is running on an endpoint—through phishing, exploitation, or supply chain
    compromise—the attacker’s next logical step is to evade or disable the watchdog that might expose their presence.

    There are three common objectives when targeting EDRs:

    1. Blinding: Suspending or freezing telemetry collection so that malicious actions occur undetected.
    2. Tampering: Modifying EDR configuration, unloading drivers, or corrupting logs to erase compromise.
    3. Bypassing: Operating entirely in areas the EDR cannot see—such as within trusted processes or in kernel contexts where user-mode protections do not apply.

    Historically, attackers have used vulnerable signed drivers, privilege escalation exploits, or direct kernel manipulation to disable EDRs. These methods, however, have become
    riskier and more detectable as Microsoft and security vendors tightened driver signing and integrity protections. As a result, researchers and adversaries alike are increasingly investigating
    user-mode techniques that do not require elevated privileges or kernel access.

    The Shift Toward User-Mode Evasion

    User-mode bypasses are attractive because they exploit legitimate system functionality rather than explicit vulnerabilities. They allow attackers to achieve stealth and persistence without triggering kernel-level defenses.

    Windows provides a vast ecosystem of legitimate executables and services—many of them digitally signed and trusted—that can be co-opted for malicious purposes. Utilities such as
    WerFault.exe (Windows Error Reporting), rundll32.exe, or msbuild.exe are prime examples: they are part of the operating system, operate under normal user privileges, and are excluded
    from strict policy enforcement.

    By exploiting these trusted processes, attackers can “live off the land,” blending their activity into normal system behavior. The EDR-Freeze technique belongs to this emerging class of
    attacks. It uses the Windows Error Reporting subsystem to temporarily suspend EDR processes from user mode, sidestepping the need for administrative control or kernel-level
    exploitation.

    Why This Matters

    When EDR visibility is disrupted, even briefly, the enterprise loses situational awareness. During that “frozen” window, attackers can execute payloads, harvest credentials, or
    establish persistence mechanisms that remain invisible once monitoring resumes.

    The key insight is that blind spots matter more than downtime—a few seconds of lost telemetry can translate into a permanent breach of foothold. This is why understanding user-
    mode evasion techniques like EDR-Freeze is critical for defenders. It highlights the need for layered prevention, least privilege, and isolation-based controls that maintain
    protection even when visibility falters.

    What is EDRFreeze (in one minute)

    EDR‑Freeze is a research proof of concept and methodology that abuses legitimate Windows Error Reporting behavior to place an endpoint security process into a temporary, suspended
    “coma” – all from user mode and without loading a vulnerable driver.

    How it works (high level):

    • It Leverages WerFaultSecure.exe (a protected component of Windows Error Reporting) to drive a call to MiniDumpWriteDump, which causes the target process threads
      to be paused while a crash dump is generated.
    • The technique Introduces a race condition: the attacker suspends exe at the precise moment the target (e.g., an EDR or AV process) is paused by the dump operation. Because the
      dump handler is itself suspended, the target remains stuck indefinitely in a suspended state rather than being resumed.
    • The entire sequence is executed in user mode. No kernel exploit, no vulnerable signed driver (BYOVD), and no direct tampering with kernel components.

     

    Why this is notable:

    This is fundamentally an abuse of legitimate OS components rather than a classical vulnerability in an EDR product.  It does not corrupt the agent or its files. It simply exploits how
    Windows handles crash reporting and process suspension to create a short (but potentially critical) blind spot.

    Immediate defender takeaway:
    Treat EDR-Freeze as a signal that attackers can weaponize trusted Windows plumbing. Effective defenses focus on detecting and constraining misuse of WER-related binaries, hardening
    process privileges/relationships, and ensuring isolation so that temporary sensor blind spots do not equate to a successful compromise.

    Why these matters

    1. User‑mode evasion: Many EDR bypasses rely on kernel tricks or vulnerable drivers. EDR‑Freeze avoids that, shrinking attacker friction.
    2. Sensor blindness window: Even a short suspension can create a gap where malicious actions may go unseen.
    3. Default tooling: The building blocks (WER, WerFaultSecure, MiniDumpWriteDump) are built into Windows.

     

    How is this different from BYOVD?

    Aspect EDR‑Freeze BYOVD (classic)
    Privilege requirements User mode orchestration, leverages PPL context of WerFaultSecure Requires kernel driver execution
    Artifacts & risk Fewer kernel artifacts; relies on legitimate Windows binaries Driver drops, install, and cleanup raise risk and telemetry
    Stealth Potentially stealthier; masquerades as WER activity Driver loading can be noisy and policy‑blocked

    Takeaway: Defenses focused solely on blocking driver‑based tampering will not fully cover techniques like EDR‑Freeze.

    What defenders can do right now

    1) Hunt & detect suspicious WER usage

    Create detections for:

    • exe invoked in contexts targeting EDR/AV PIDs (e.g., Defender’s MsMpEng) or LSASS.
    • Abnormal command‑line usage or parent/child relationships spawning exe just prior to security agent stalls.
    • A protected exe process being suspended or tampered with (where telemetry supports it).

    Tip: Community rules are already emerging. Look for Sigma/EDR analytics that flag WER‑based process freezing patterns.

    2) Reduce the blast radius

    • Least privilege on endpoints: Ensure users are not local admins; restrict debug privileges where possible.
    • Exploit surface reduction: Block or tightly control access to DbgHelp/MiniDumpWriteDump in user environments where feasible, especially on servers.
    • Application control: Constrain who can execute or spawn exe or similar diagnostic binaries.

    3) Harden and instrument security agents

    • Verify that your EDR/AV has self‑protection against thread suspension/diagnostic abuse.
    • Monitor gaps in heartbeat/telemetry that correlate with WER activity.
    • Pressure‑test with tabletop or controlled lab exercises that simulate an EDR suspension window.

    4) Add isolation so “blind spots” do not equal compromise

    Even if visibility dips momentarily, contain risky actions:

    • Open untrusted websites and documents in an isolated workspace.
    • Apply content sanitization (CDR) and download controls, so payloads never gain a foothold.
    • Keep sensitive files in protected local vaults with on‑host classification to mitigate exfiltration/ransomware if monitoring falters for a few seconds.

    Where BUFFERZONE® fits

    BUFFERZONE® Safe Workspace® isolates browsers and office apps locally, keeping any untrusted code and files confined. Our privacy‑preserving Safe Data engine auto‑classifies
    sensitive files and locks them down on the endpoint. Together, these controls:

    • Prevent malware execution and data movement during an EDR visibility gap.
    • Contain untrusted code even if it attempts to exploit user‑mode tricks like WER abuse.
    • Reduce dwell time and the operational value that attackers gain from short “freeze” windows.

    We view EDR‑Freeze as another reminder that prevention and isolation are essential companions to detection.

    FAQ for security leaders

    Is this a Windows vulnerability?

    Not in the traditional sense. It is an abuse of intended behaviors (WER + dump API) via clever timing.

    Does Microsoft Defender block it?

    Microsoft has stated that attempts are detected and blocked in Defender. Defense‑in‑depth is still advised across heterogeneous fleets.

    Should I block WER?

    Generally, no; it helps reliability and support. Instead, monitor and restrict suspicious invocations, especially those targeting security processes.

    What about servers?

    Servers are prime targets for living‑off‑the‑land abuse. Emphasize the least privilege, application control, and WER analytics on Tier‑0/Tier‑1 assets.

    A quick action checklist

    • Add detections for exe targeting EDR/AV/LSASS PIDs.
    • Alert on unusual WER command lines and on suspension of events around security processes.
    • Validate your EDR’s self‑protection against thread suspension.
    • Re‐affirm privilege and debug rights restrictions.
    • Expanded isolation/CDR coverage for browsers, email, and office documents.
    • Classify and vault sensitive data on endpoints.

     

    Last thoughts

    EDR‑Freeze does not “break” your EDR; it exploits a narrow, time‑bound condition in Windows diagnostics. The best response is layered controls that assume momentary sensor
    gaps in their own diagnostics. The best response is layered controls that assume momentary sensor gaps and still protect what matters. Combine instrumentation, hardening, and isolation to deny attackers’ value, even when they are clever with user‑mode tricks.