CVE-2025-8302

Executive Summary

CVE-2025-8302 is a critical heap-based buffer overflow vulnerability in the Realtek rtl81xx SDK Wi-Fi Driver (rtwlanu). The flaw resides in the N6CSet_DOT11_CIPHER_DEFAULT_KEY function, which fails to validate the length of user-supplied data before copying it to a fixed-length heap buffer. An attacker with low-privileged code execution on the target system can exploit this to escalate privileges to SYSTEM and execute arbitrary code. The CVSS score is 8.8 (High), and no public exploit or patch is currently available. This vulnerability is particularly dangerous in enterprise environments where Wi-Fi drivers are commonly deployed on Windows systems.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a hardware driver component (Realtek rtl81xx SDK) distributed by Realtek and integrated by OEMs. Supply chain risk is elevated due to the lack of a vendor patch and the widespread use of Realtek Wi-Fi chipsets in laptops, desktops, and embedded systems.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Base Score: 8.8 (High)
• Attack Vector: Local (AV:L) – requires local access to the system.
• Attack Complexity: Low (AC:L) – no special conditions needed.
• Privileges Required: Low (PR:L) – attacker needs initial low-privileged code execution.
• User Interaction: None (UI:N) – no user action required.
• Scope: Unchanged (S:U) – exploitation stays within the same security authority.
• Confidentiality Impact: High (C:H) – full data compromise possible.
• Integrity Impact: High (I:H) – arbitrary code execution as SYSTEM.
• Availability Impact: High (A:H) – potential for denial of service or system crash.

Threat Level: Critical for environments with Realtek Wi-Fi drivers. The lack of a patch and the ability to escalate to SYSTEM makes this a high-priority target for attackers.

Deep Dive & Mechanics

The vulnerability is a classic heap-based buffer overflow in the N6CSet_DOT11_CIPHER_DEFAULT_KEY function of the Realtek rtwlanu driver. This function is responsible for setting the default cipher key for 802.11 wireless security. The driver does not properly validate the length of user-supplied data (likely a key material buffer) before copying it to a fixed-length heap buffer. An attacker can supply an oversized key, causing a heap overflow that corrupts adjacent memory structures.

Root Cause: Missing bounds check on the input length parameter. The function likely uses memcpy or similar without verifying that the source data fits within the destination buffer.

Exploitation Path:

1. Attacker gains low-privileged code execution (e.g., via a user-mode application or script).
2. Attacker sends a crafted IOCTL (Input/Output Control) request to the rtwlanu driver, triggering the vulnerable function with an oversized key.
3. The heap overflow corrupts adjacent heap metadata or function pointers.
4. Attacker leverages the corruption to achieve arbitrary code execution in kernel context (SYSTEM).
5. Full system compromise.

Impact: Complete takeover of the affected system, including data theft, malware installation, and lateral movement.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the N6CSet_DOT11_CIPHER_DEFAULT_KEY function. A patched version would include a length check before the copy operation.

Vulnerable Code (Conceptual):

void N6CSet_DOT11_CIPHER_DEFAULT_KEY(ULONG KeyLength, PUCHAR KeyData) {
    PUCHAR buffer = (PUCHAR)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 32);
    // Missing length validation
    memcpy(buffer, KeyData, KeyLength); // Overflow if KeyLength > 32
}

Patched Code (Conceptual):

void N6CSet_DOT11_CIPHER_DEFAULT_KEY(ULONG KeyLength, PUCHAR KeyData) {
    if (KeyLength > 32) {
        return STATUS_INVALID_PARAMETER; // Reject oversized input
    }
    PUCHAR buffer = (PUCHAR)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 32);
    memcpy(buffer, KeyData, KeyLength);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Target system with Realtek rtl81xx Wi-Fi driver (rtwlanu) installed.
• Low-privileged code execution capability (e.g., via a user-mode process).
• Knowledge of the IOCTL code used to invoke N6CSet_DOT11_CIPHER_DEFAULT_KEY.

Exploitation Steps:

1. Reconnaissance: Identify the vulnerable driver version and IOCTL interface using tools like WinObj or custom enumeration.
2. Craft Payload: Create a heap overflow payload that overwrites a function pointer or heap metadata to redirect execution to shellcode.
3. Trigger: Send the crafted IOCTL from user mode to the driver.
4. Escalate: The overflow leads to arbitrary code execution as SYSTEM.

Example (Conceptual):

// User-mode exploit skeleton
HANDLE hDevice = CreateFile(L"\\\\.\\rtwlanu", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
if (hDevice == INVALID_HANDLE_VALUE) return;

// Craft oversized key buffer
char keyData[256] = {0};
// Fill with shellcode and ROP chain
DWORD bytesReturned;
DeviceIoControl(hDevice, IOCTL_SET_DEFAULT_KEY, keyData, sizeof(keyData), NULL, 0, &bytesReturned, NULL);

Note: No public exploit code is available. This is a conceptual example.

Blue Team

Detection:

• Monitor for unusual IOCTL calls to the rtwlanu driver, especially with large input buffers.
• Use Sysmon to log process creation and driver load events.
• Enable Windows Event Logging for kernel driver operations.

Mitigation:

• Apply vendor patch when available.
• Restrict local user privileges to prevent low-privileged code execution.
• Use application whitelisting to block untrusted executables.
• Deploy endpoint detection and response (EDR) solutions with behavioral analysis.

Indicators of Compromise (IOCs)

• File Hashes: Unknown (no public samples).
• Registry Keys: HKLM\SYSTEM\CurrentControlSet\Services\rtwlanu (driver service).
• Network: No network-based IOCs (local exploit).
• Process: rtwlanu.sys loaded in kernel memory.
• Behavior: Unusual IOCTL calls with large buffers to the driver device \\.\rtwlanu.

Detection Engineering

YARA Rule

rule CVE_2025_8302_Realtek_Heap_Overflow {
    meta:
        description = "Detects potential exploitation of CVE-2025-8302 in Realtek rtwlanu driver"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-8302"
    strings:
        $s1 = "N6CSet_DOT11_CIPHER_DEFAULT_KEY" ascii wide nocase
        $s2 = "rtwlanu" ascii wide nocase
        $s3 = "IOCTL" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-8302 Realtek rtwlanu Heap Overflow Exploitation
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects suspicious IOCTL calls to the Realtek rtwlanu driver indicative of CVE-2025-8302 exploitation.
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 11  # FileCreate
        TargetFilename|contains: 'rtwlanu.sys'
    condition: selection
falsepositives:
    - Legitimate driver updates
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2025-8302 Realtek rtwlanu Heap Overflow Attempt"; content:"|00 00 00 00|"; depth:4; offset:0; classtype:attempted-admin; sid:1000001; rev:1;)

Note: This is a placeholder; actual detection requires kernel-level monitoring.

Remediation & Mitigation

Immediate Actions:

1. Isolate affected systems from untrusted networks if possible.
2. Restrict local user privileges to prevent initial low-privileged code execution.
3. Monitor for suspicious driver activity using EDR tools.

Long-term Fix:

• Await an official patch from Realtek. Contact Realtek support for updates.
• Consider replacing Realtek Wi-Fi hardware with a vendor that provides timely security patches.
• Implement driver blocklisting or use Windows Defender Application Control (WDAC) to prevent loading vulnerable driver versions.

Workaround:

• Disable the Realtek Wi-Fi driver if not essential, or use a different network interface.

Valters IT