CVE-2021-22280

Executive Summary

CVE-2021-22280 is a high-severity local privilege escalation vulnerability affecting B&R Automation Studio versions 4.0 through 4.11. The flaw resides in improper DLL loading algorithms, allowing an authenticated local attacker to execute arbitrary code in the context of the product. With a CVSS score of 7.2, this vulnerability requires local access and authentication, but no user interaction, making it a significant threat in industrial control system (ICS) environments where multiple users share workstations. The EPSS score of 0.0% indicates low exploitation likelihood in the wild, but the lack of a confirmed patch (status UNKNOWN/UNPATCHED) elevates the risk for organizations relying on this software.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby ecosystems. It is a proprietary industrial software package from B&R Automation, distributed via their official channels. The supply chain risk is limited to the integrity of the software installation media and the trustworthiness of the vendor’s update mechanism.

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: 7.2 (High)
• Attack Vector: Local (AV:L) – requires physical or remote desktop access to the system.
• Attack Complexity: Low (AC:L) – no special conditions needed.
• Privileges Required: Low (PR:L) – attacker must have a valid user account on the system.
• User Interaction: None (UI:N) – no victim action required.
• 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) – arbitrary code execution.
• Availability Impact: High (A:H) – potential for denial of service.

Threat Level: High. While local access is required, in shared ICS environments (e.g., engineering workstations), this vulnerability can be exploited by any authenticated user to escalate privileges and compromise the entire system.

Deep Dive & Mechanics

The vulnerability stems from improper DLL loading algorithms in B&R Automation Studio. When the application loads dynamic-link libraries (DLLs), it does not securely validate the search path. An authenticated local attacker can place a malicious DLL in a directory that the application searches before the legitimate system directory (e.g., the current working directory or a user-writable path). This is a classic DLL hijacking scenario (CWE-427: Uncontrolled Search Path Element).

Attack Flow:

1. Attacker gains low-privileged access to the target system (e.g., via compromised credentials or physical access).
2. Attacker identifies a DLL that Automation Studio loads without a fully qualified path.
3. Attacker places a malicious DLL with the same name in a directory that is searched first (e.g., the application’s working directory or a user-writable folder in the PATH).
4. When Automation Studio starts or performs a specific action, it loads the attacker’s DLL instead of the legitimate one.
5. The malicious DLL executes arbitrary code in the context of the Automation Studio process, which typically runs with elevated privileges.

Affected Versions: >=4.0 and <4.12. Version 4.12 is the first patched release, but the patch status is marked as UNKNOWN/UNPATCHED in the provided data, indicating that the vendor may not have released a fix or the patch is not publicly confirmed.

Vulnerable vs. Patched Code

Since no patch details are available, we can only describe the vulnerable behavior generically.

Vulnerable Code (Conceptual):

// Vulnerable: Uses relative path or unsafe search order
HMODULE hModule = LoadLibrary(L"helper.dll"); // No full path

Patched Code (Expected):

// Patched: Uses absolute path or safe DLL search mode
HMODULE hModule = LoadLibraryEx(L"C:\\Program Files\\B&R\\Automation Studio\\helper.dll", NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);

The patched version should either specify the full path to the DLL or use SetDllDirectory to restrict the search path to safe directories only.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a Windows system running B&R Automation Studio version 4.0 to 4.11.
• A valid user account (low-privileged).
• Knowledge of a DLL that Automation Studio loads unsafely (e.g., msvcp140.dll, vcruntime140.dll, or a custom B&R DLL).

Exploitation Steps:

1. Identify vulnerable DLL: Use Process Monitor (Procmon) to filter for CreateFile operations by AutomationStudio.exe and look for NAME NOT FOUND results in user-writable directories.
2. Craft malicious DLL: Create a DLL that exports the same functions as the target DLL but includes malicious payload (e.g., reverse shell, privilege escalation).
3. Place DLL: Copy the malicious DLL to a directory that is searched before the system directory (e.g., C:\Users\<username>\AppData\Local\Temp\ or the application’s install directory if writable).
4. Trigger load: Restart Automation Studio or perform an action that loads the DLL.
5. Execute payload: The malicious DLL runs with the privileges of Automation Studio (often high integrity).

Example Malicious DLL Code (C++):

// malicious.cpp
#include <windows.h>
#pragma comment(lib, "ws2_32.lib")

BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) {
    if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
        // Execute reverse shell or privilege escalation
        system("net localgroup Administrators attacker /add");
    }
    return TRUE;
}

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

Blue Team (Detection & Defense)

Detection Steps:

1. Monitor DLL loads: Use Sysmon Event ID 7 (Image loaded) to detect unexpected DLLs loaded by AutomationStudio.exe from user-writable paths.
2. File integrity monitoring: Alert on new DLL files created in directories like %TEMP%, %APPDATA%, or the application directory.
3. Process auditing: Enable command-line auditing to capture any suspicious commands executed by Automation Studio.

Defense Measures:

• Apply the principle of least privilege: Run Automation Studio with a dedicated service account that has minimal permissions.
• Use AppLocker or Windows Defender Application Control (WDAC) to block execution of unsigned DLLs from user-writable paths.
• Enable Safe DLL Search Mode via registry: HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\SafeDllSearchMode = 1.
• Monitor for known vulnerable versions and apply vendor patches when available.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Placeholder – actual hashes depend on the malicious DLL)
  • malicious.dll: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Process Anomalies:
  • AutomationStudio.exe loading DLLs from C:\Users\*\AppData\Local\Temp\*
  • AutomationStudio.exe spawning cmd.exe or powershell.exe
• Registry Changes:
  • Creation of HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run entries pointing to user-writable paths.
• Network Connections:
  • Outbound connections from AutomationStudio.exe to unknown IPs (if reverse shell used).

Detection Engineering

YARA Rule

rule CVE_2021_22280_DLL_Hijack {
    meta:
        description = "Detects malicious DLLs targeting B&R Automation Studio DLL hijacking vulnerability"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2021-22280"
    strings:
        $s1 = "AutomationStudio.exe" nocase
        $s2 = "LoadLibrary" nocase
        $s3 = "helper.dll" nocase  // Example vulnerable DLL name
    condition:
        $s1 and $s2 and $s3
}

Sigma Rule

title: CVE-2021-22280 - B&R Automation Studio DLL Hijacking
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects suspicious DLL loads by AutomationStudio.exe from user-writable directories
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2021-22280
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 7
        Image|endswith: '\AutomationStudio.exe'
        ImageLoaded|contains:
            - '\AppData\Local\Temp\'
            - '\AppData\Roaming\'
            - '\Users\'
    condition: selection
falsepositives:
    - Legitimate DLLs placed in user directories by IT administrators
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2021-22280 - Potential B&R Automation Studio DLL Hijack Outbound";
    flow:to_server,established;
    content:"AutomationStudio.exe"; nocase;
    content:"|2e|dll|2e|"; distance:0;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: Update B&R Automation Studio to version 4.12 or later if a patch is available. Check the vendor’s official site for the latest version.
2. Workaround: If patching is not possible, restrict local user permissions on engineering workstations. Use Group Policy to enforce Safe DLL Search Mode.
3. Monitor: Deploy the YARA and Sigma rules above to detect exploitation attempts.

Long-Term Measures:

• Implement application whitelisting (e.g., WDAC) to block unauthorized DLLs.
• Conduct regular vulnerability scans of ICS assets.
• Train users to avoid running untrusted software on engineering workstations.

Patch Status: UNKNOWN/UNPATCHED – Contact B&R support for official patch information.

Valters IT