CVE-2021-40424

Executive Summary

CVE-2021-40424 is an out-of-bounds read vulnerability in the Webroot Secure Anywhere security product, specifically affecting version 21.4. The flaw resides in the IOCTL handlers GetProcessCommand and B_03 within the device driver component, triggered via a specially crafted executable that issues a local IOCTL request. Successful exploitation results in a denial of service condition, likely causing the driver or the system to crash due to an unhandled out-of-bounds memory read. The vulnerability is unpatched, and no public exploit code or in-the-wild exploitation evidence has been identified at the time of writing. Given the local attack vector and the absence of patch availability, affected enterprise endpoints running Webroot Secure Anywhere version 21.4 remain exposed to local denial-of-service attacks.

Technical Analysis

The vulnerability is a classic out-of-bounds read flaw, classified under CWE-125. The affected component is the kernel-mode device driver WRCore_x64 used by Webroot Secure Anywhere 21.4. The driver exposes an IOCTL interface to user-mode applications, enabling them to request system-level operations such as querying process command lines.

The NVD description identifies two distinct IOCTL code paths as vulnerable:

1. GetProcessCommand — a handler that retrieves the command-line parameters of a process. The out-of-bounds read occurs when the handler processes a request without adequately validating the length or boundaries of the input buffer supplied by the caller.
2. B_03 — a secondary IOCTL handler with an undocumented purpose that exhibits the same out-of-bounds read weakness.

Attack Mechanism:

The vulnerability is triggered via an IOCTL request issued from a specially crafted user-mode executable. The core problem is a missing bounds check on the input buffer length or the requested operation size. When the driver processes the IOCTL, it attempts to read beyond the allocated buffer size, which may cause the driver to access unmapped or invalid memory regions.

Attack Surface:

• Attack Vector: Local (requires the attacker to execute code on the target system with at least medium integrity level, though no privilege requirement is specified in the CVSS vector).
• Attack Complexity: Low — no special conditions beyond being able to run a program and call the vulnerable IOCTL.
• Privileges Required: None per the CVSS vector, suggesting any local user can trigger the vulnerability.
• User Interaction: None required.

Code-Level Considerations:

The NVD description mentions the IOCTL request GetProcessCommandLine in its second sentence despite the title naming GetProcessCommand. This suggests that within the driver's dispatch table, the GetProcessCommand handler is likely aliased or directly associated with the GetProcessCommandLine functionality. The driver presumably lacks a proper ProbeForRead call, or fails to validate the SystemBuffer or Type3InputBuffer length against the expected size, leading to a buffer over-read condition.

Concurrency Note: The vulnerability does not describe a race condition; it is a deterministic flaw triggered by a single malicious IOCTL call with an undersized buffer.

Limitations of Available Technical Detail: The NVD description does not provide the exact IOCTL code values, the structure of the input/output buffers, or the precise assembly-level instructions that perform the out-of-bounds read. Without these details, the vulnerability must be treated at the class level: a local unprivileged user can invoke a driver IOCTL that triggers an invalid memory read, causing a system or driver crash (BSOD on Windows).

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class.

Step 1: Reconnaissance / Target Identification

An attacker with local access to a machine running Webroot Secure Anywhere 21.4 first identifies the presence of the vulnerable driver. This can be accomplished by:

• Enumerating loaded kernel modules (driverquery or sc query).
• Checking the version of Webroot Secure Anywhere installed.
• Verifying that WRCore_x64.sys is loaded in kernel memory.

Step 2: Triggering the Vulnerability

The attacker crafts a small executable that:

1. Opens a handle to the Webroot driver device (e.g., \\.\WRCore_x64 or similar device name established by the driver's control device object).
2. Allocates an intentionally undersized input buffer.
3. Calls DeviceIoControl with the vulnerable IOCTL code (GetProcessCommand or B_03), passing the small buffer as input.

Step 3: Payload / Execution Method

At the vulnerability-class level, the malicious executable causes the driver's IRP handler to process the IOCTL. The handler attempts to read a fixed-size structure (e.g., a PROCESS_COMMAND_LINE structure) from the user-supplied buffer. Because the buffer is shorter than the expected structure size, the driver reads past the end of the allocated buffer into adjacent memory.

Step 4: Post-Exploitation Impact — Denial of Service

• Immediate Effect: The out-of-bounds read either crashes the driver directly (via an access violation in kernel mode, triggering a Blue Screen of Death) or causes the Webroot service to malfunction, becoming unresponsive.
• System Impact: If the driver crashes, the system may require a reboot. If the driver is part of the boot-start driver set or the security suite's self-protection mechanism, the system may be left in an unprotected or unstable state, or fail to fully boot.
• Persistence of Impact: The DoS is transient in nature — the system recovers after reboot — but the attacker can re-trigger the crash at will, enabling repeated denial-of-service campaigns against the endpoint.

Alternate Scenario — Weaponized Malware: An attacker who has already compromised a system with low-privilege code could leverage this vulnerability to destabilize the security agent, disabling or crashing the host-based security control before performing further malicious activity.

Impact Assessment

The CVSS score of 7.1 (High) is driven primarily by the confidentiality impact subscore of High (C:H/I:N/A:L), indicating that the out-of-bounds read could potentially disclose sensitive kernel memory contents to the attacker, though the primary documented impact is denial of service. The availability impact is rated Low (A:L).

Business Impact:

• Confidentiality: The out-of-bounds read may allow a local attacker to read small amounts of kernel memory, which could contain sensitive data such as pointers, hashes, or other security-relevant information — though no information-disclosure exploit has been demonstrated publicly.
• Availability: The primary documented impact is DoS. An attacker can repeatedly crash the Webroot driver and/or the host system, degrading endpoint stability.
• Integrity: No integrity impact (I:N) per the CVSS vector.

Affected Systems:

• All endpoints running Webroot Secure Anywhere version 21.4 on Windows (64-bit architecture, given the driver name WRCore_x64).
• The affected version list provided in the intelligence data is empty, meaning no patched version has been confirmed to resolve this issue.

Blast Radius:

• Local only. The vulnerability is not remotely exploitable. However, in enterprise environments where local users are not fully trusted, this flaw enables any local user to crash the security software, creating a gap in endpoint protection.

Patch Confidence Assessment: With patch confidence rated 0/4, there is no evidence that Webroot has released a fix. Enterprise deployments remain exposed indefinitely, and monitoring for an eventual patch is critical.

Detection Guidance

Sigma Rule

title: Webroot SecureAnywhere IOCTL Out-of-Bounds Read Exploitation
id: b0a3c21e-5f6a-4c9e-8a2b-3d4e5f6a7b8c
status: experimental
description: Detects calls to the Webroot WRCore_x64 driver IOCTL handlers associated with CVE-2021-40424 (GetProcessCommand / B_03 handler).
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2021-40424
author: Valtersit Security Research
date: 2025/01/18
logsource:
    category: process_creation
    product: windows
detection:
    selection_executable:
        Image|endswith:
            - '\program.exe'
            - '\test.exe'
            - '\poc.exe'
    selection_deviceiocontrol:
        CommandLine|contains:
            - 'DeviceIoControl'
            - 'WRCore'
            - '\.\WRCore'
    condition: selection_executable and selection_deviceiocontrol
falsepositives:
    - Legitimate Webroot management tools issuing normal IOCTL calls
    - Administrative scripts that interact with the driver
level: high

YARA Rule

rule Webroot_CVE_2021_40424_IOCTL_Exploit
{
    meta:
        author = "Valtersit Security Research"
        description = "Detects binaries that reference the Webroot WRCore driver IOCTL calls associated with CVE-2021-40424"
        cve = "CVE-2021-40424"
        date = "2025-01-18"
        severity = "high"
    strings:
        $s1 = "WRCore_x64" ascii wide
        $s2 = "\\\\.\\WRCore" ascii wide
        $s3 = "GetProcessCommand" ascii wide
        $s4 = "B_03" ascii wide
        $s5 = "DeviceIoControl" ascii wide
        $s6 = { 48 8B 05 ?? ?? ?? ?? 48 8D 0D ?? ?? ?? ?? E8 ?? ?? ?? ?? }  // typical DeviceIoControl call pattern (common x64 prologue)
    condition:
        uint16(0) == 0x5A4D and  // MZ header
        (2 of ($s1, $s2, $s3, $s4) or ($s5 and $s6))
}

Suricata IDS Rule

alert ip any any -> any any (msg:"CVE-2021-40424 - Webroot IOCTL Out-of-Bounds Attempt"; flow:to_server; content:"WRCore"; nocase; content:"DeviceIoControl"; nocase; pcre:"/\\\\.\\WRCore[^\"]*/i"; classtype:attempted-dos; sid:20240101; rev:1; reference:cve,2021-40424;)

Note: As this vulnerability is triggered locally via a native API, network signatures have extremely limited detection value. The rule above detects outbound network traffic from a compromised host that might exfiltrate data from a known Webroot-related tool, but it will NOT detect the actual exploitation. Network monitoring is not a recommended primary detection channel for this CVE.

Elastic Detection

// Query for suspicious process activity involving Driver Communication
// Look for processes that name the WRCore driver AND call DeviceIoControl
sequence by process.entity_id
  [process where event.action == "start" and
     process.name : ("cmd.exe", "powershell.exe", "rundll32.exe", "*.exe")
     and process.command_line : ("*WRCore*", "*\\.\\WRCore*")
  ]
  [process where event.action == "start" and
     process.command_line : ("*DeviceIoControl*")
  ]

Splunk SPL Query

index=windows sourcetype=WinEventLog:Security OR sourcetype=XmlWinEventLog
| search "WRCore" OR "\\\\.\\WRCore" OR "GetProcessCommand"
| eval is_suspicious=if(match(CommandLine, "(?i)DeviceIoControl") AND match(CommandLine, "(?i)WRCore"), 1, 0)
| where is_suspicious=1
| table _time, host, user, process_name, CommandLine, parent_process
| sort -_time

Wazuh OSSEC Rule

<rule id="100410" level="10">
    <if_sid>550</if_sid>
    <match>WRCore_x64</match>
    <description>CVE-2021-40424 - Potential Webroot IOCTL out-of-bounds read exploitation attempt detected. Local process referencing WRCore driver.</description>
    <group>cve-2021-40424,webroot,denial_of_service,windows,</group>
    <mitre>
        <id>T1068</id>
    </mitre>
</rule>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No vendor fix has been identified from any tracked source. The following recommendations are based on the vulnerability class and current product behavior.

1) Immediate Mitigations (No Patch Available):

• Restrict local code execution: Reduce the attack surface by enforcing application allow-listing (e.g., AppLocker / WDAC) to prevent untrusted binaries from running on endpoints.
• Limit local user privileges: Minimize the number of users with interactive logon sessions on critical servers. Every local user is a potential attacker given the local attack vector and the CVSS score reflecting no privilege requirement.
• Monitor for system crashes: Enable memory dump collection (kernel and complete memory dumps) and centrally collect .dmp files and WER (Windows Error Reporting) events. If WRCore_x64.sys appears as the faulting module repeatedly, treat that as a potential exploitation indicator.
• Isolate high-value endpoints: For systems where availability is critical, consider whether Webroot Secure Anywhere 21.4 can be moved into a restricted VLAN or isolated environment until a fix is available.
• Consider alternative security controls: As a contingency, evaluate whether the Webroot agent on sensitive endpoints can be temporarily replaced with a competing product that has an active patch status for similar known CVEs.

2) Patch / Upgrade Steps:

• Subscribe to Webroot's security advisories and monitor the vendor's patch release notes. No fixed version has been identified.
• When a patch is released, deploy it via the Webroot Management Console to all endpoints. Prioritize high-value servers and endpoints running version 21.4.
• After patch installation, verify the driver version has changed by checking the file version metadata of WRCore_x64.sys.
• If no patch is released in a reasonable timeframe, plan for a coordinated migration to a newer Webroot product line (e.g., Webroot Business Endpoint Protection latest version) that is not affected.

3) Long-Term Hardening:

• Enable Windows Credential Guard and Virtualization-Based Security (VBS): This reduces the impact of kernel-mode flaws by isolating critical system secrets, though it does not prevent the OOB read itself.
• Implement the principle of least privilege: Ensure standard users cannot load arbitrary kernel drivers or execute privileged IOCTL calls.
• Harden the endpoint with Attack Surface Reduction (ASR) rules: Block child process creation from Office applications and other common malware vectors to reduce the likelihood of a local attacker successfully executing the crafted exploit binary.
• Regularly review vendor security advisories: The lack of a patch means that the advisory should be re-checked at least monthly. Track the CVE in a vulnerability management platform (e.g., a ticketing system with an SLA for vendor communication).
• Test backup/restore procedures: Ensure that a clean system image can be restored quickly if the webroot driver crash leads to a boot failure or kernel panic state.

Summary: The vulnerability is unpatched, locally exploitable, and enables denial of service. Enterprise teams should focus on restricting local execution, monitoring for crashes of WRCore_x64.sys, and watching for Webroot's official fix.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2021-40424
2. CWE-125 (Out-of-bounds Read): https://cwe.mitre.org/data/definitions/125.html
3. Webroot Product Page (for version identification): https://www.webroot.com/us/en/business/small-business/products/endpoint-protection
4. MITRE ATT&CK Technique T1068 (Exploitation for Privilege Escalation): https://attack.mitre.org/techniques/T1068/
5. CISA Known Exploited Vulnerabilities Catalog (confirming this CVE is NOT listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat Actor Activity: No known threat actor campaigns have been publicly attributed to this CVE. CISA KEV does not include it, and no exploit-in-the-wild evidence has been reported at the time of this report.