CVE-2025-10214

Executive Summary

CVE-2025-10214 is a DLL search path hijacking vulnerability affecting UPDF.exe version 1.8.5.0 for Windows. The vulnerability allows an attacker with local access to execute arbitrary code by placing a malicious FREngine.dll file in the user's application data directory (C:/Users/<user>/AppData/Local/UPDF/FREngine/Bin64/). This can lead to arbitrary code execution and persistence on the compromised system. The vulnerability is currently unpatched, and no official fix has been released by the vendor.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD) / 7.8 (Estimated)
• 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)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)
• Threat Level: High – Exploitation requires local access but can lead to full system compromise.

Deep Dive & Mechanics

The vulnerability is a classic DLL search path hijacking (CWE-427). When UPDF.exe is launched, it attempts to load the FREngine.dll library. The application's search order includes the user-writable directory C:/Users/<user>/AppData/Local/UPDF/FREngine/Bin64/ before secure system directories. An attacker with local access can place a malicious FREngine.dll in this directory. When UPDF.exe runs, it loads the attacker's DLL instead of the legitimate one, executing arbitrary code in the context of the user running UPDF.exe. This can be used for privilege escalation, persistence, or data theft.

Vulnerable vs. Patched Code

Vulnerable Code (UPDF.exe 1.8.5.0): The application uses a relative or insecure DLL search path that includes the user's AppData directory. The exact code is not publicly available, but the behavior is confirmed by the CVE description.

Patched Code: No patched version exists. A fix would involve either:

• Hardcoding the full path to the legitimate FREngine.dll in a secure system directory.
• Using SetDllDirectory to remove the current working directory from the search path.
• Digitally signing the DLL and verifying the signature before loading.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a Windows machine with UPDF.exe 1.8.5.0 installed.
• Ability to write to C:/Users/<user>/AppData/Local/UPDF/FREngine/Bin64/.

Exploit Steps:

1. Create a malicious FREngine.dll that executes a payload (e.g., reverse shell, keylogger).
2. Place the DLL in the target directory: C:/Users/<target_user>/AppData/Local/UPDF/FREngine/Bin64/FREngine.dll.
3. Wait for the user to launch UPDF.exe, or trigger it via scheduled task or other means.
4. The malicious DLL is loaded, executing arbitrary code.

Example Malicious DLL Code (C++):

// malicious.cpp
#include <windows.h>

BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
    if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
        // Execute payload, e.g., spawn calc.exe
        WinExec("calc.exe", SW_SHOW);
    }
    return TRUE;
}

Compile with: x86_64-w64-mingw32-gcc -shared -o FREngine.dll malicious.cpp

Blue Team

Detection Steps:

1. Monitor file creation events in C:/Users/*/AppData/Local/UPDF/FREngine/Bin64/FREngine.dll.
2. Monitor process creation events for UPDF.exe and check loaded DLLs.
3. Use Sysmon to log DLL load events (Event ID 7) and alert on FREngine.dll loaded from user-writable paths.
4. Enable Windows Defender Attack Surface Reduction (ASR) rules to block untrusted DLL loads.

Indicators of Compromise (IOCs)

• File: C:/Users/<user>/AppData/Local/UPDF/FREngine/Bin64/FREngine.dll (unexpected or unsigned)
• Process: UPDF.exe loading FREngine.dll from user-writable path
• Registry: N/A
• Network: Outbound connections from UPDF.exe to unknown IPs (if payload is a reverse shell)
• Hash: SHA256 of malicious FREngine.dll (varies per attacker)

Detection Engineering

YARA Rule

rule CVE_2025_10214_DLL_Hijack {
    meta:
        description = "Detects malicious FREngine.dll used in CVE-2025-10214"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "unknown"
    strings:
        $s1 = "FREngine.dll" nocase
        $s2 = "UPDF" nocase
    condition:
        $s1 and $s2 and filesize < 10MB
}

Sigma Rule

title: CVE-2025-10214 DLL Search Path Hijacking
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects UPDF.exe loading FREngine.dll from user-writable path
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 7
        ImageLoaded|endswith: '\\FREngine.dll'
        Image|endswith: '\\UPDF.exe'
    condition: selection
falsepositives:
    - Legitimate UPDF updates (rare)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2025-10214 - UPDF.exe potential DLL hijack outbound";
    flow:to_server,established;
    content:"UPDF"; http_user_agent;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Restrict write access to the C:/Users/*/AppData/Local/UPDF/FREngine/Bin64/ directory for non-admin users.
2. Monitor for unexpected FREngine.dll files in user directories.
3. Use Application Control (e.g., AppLocker, WDAC) to block unsigned DLLs from loading into UPDF.exe.

Long-term Fix:

• Vendor must release a patched version that uses a secure DLL loading mechanism (e.g., absolute path, digital signature verification).
• Until patched, consider removing or replacing UPDF.exe with an alternative PDF reader.

Workaround:

• Set the CWDIllegalInDllSearch registry key to 0xFFFFFFFF to disable current working directory in DLL search order (requires testing for compatibility).

Valters IT