CVE-2025-49797

Executive Summary

CVE-2025-49797 is a privilege escalation vulnerability in multiple Brother driver installers for Windows. The vulnerability allows an attacker with local access to execute arbitrary programs with administrative privileges. The exact affected product names, model numbers, and versions are not fully disclosed, but the vendor has provided references for further details. The CVSS score is 7.8 (High), indicating a significant risk due to the potential for full system compromise. No public proof-of-concept (PoC) or exploit code is currently available, and the patch status is unknown.

CVSS Breakdown & Threat Level

• CVSS Score: 7.8 (High)
• 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) – The attacker must have local access to the system.
• Attack Complexity: Low (AC:L) – No special conditions are required for exploitation.
• Privileges Required: Low (PR:L) – The attacker needs initial user-level access.
• User Interaction: None (UI:N) – No user action is required beyond the attacker’s own actions.
• Scope: Unchanged (S:U) – The vulnerability does not affect resources beyond the vulnerable component.
• Confidentiality Impact: High (C:H) – Full disclosure of sensitive data is possible.
• Integrity Impact: High (I:H) – The attacker can modify system files or configurations.
• Availability Impact: High (A:H) – The attacker can cause a denial of service or system crash.

Threat Level: High. The vulnerability allows a low-privileged attacker to gain full administrative control, leading to complete system compromise.

Deep Dive & Mechanics

The vulnerability resides in the installer components of Brother printer/scanner drivers for Windows. During the installation process, the installer runs with elevated privileges (SYSTEM or Administrator). Due to improper handling of file operations or command execution, a low-privileged attacker can exploit a race condition, symbolic link attack, or insecure DLL loading to escalate privileges.

Potential Attack Vector:

1. DLL Hijacking: The installer may load a DLL from a user-writable directory (e.g., the user’s Temp folder) instead of a secure system path. An attacker can place a malicious DLL in that location before the installer runs.
2. Symbolic Link Attack: The installer may create or write to a file in a location where the attacker can create a symbolic link pointing to a critical system file (e.g., C:\Windows\System32\config\SAM). When the installer writes to the link, it overwrites the target file.
3. Command Injection: The installer may execute a command with user-controlled parameters without proper sanitization, allowing the attacker to inject additional commands.

The exact mechanism is not publicly documented, but the high CVSS score and the nature of driver installers suggest a file-based or process-based privilege escalation.

Vulnerable vs. Patched Code

Since no patch details are available, a generic comparison is provided:

Vulnerable Code Pattern (C++ example):

// Insecure: Loads DLL from user-writable path
HMODULE hMod = LoadLibrary(L"C:\\Users\\Public\\Temp\\helper.dll");
if (hMod) {
    // Execute function from DLL
}

Patched Code Pattern:

// Secure: Loads DLL from system-protected path
HMODULE hMod = LoadLibrary(L"C:\\Windows\\System32\\helper.dll");
if (hMod) {
    // Execute function from DLL
}

The patched version would ensure that all file operations use absolute paths within protected directories, validate digital signatures, and drop privileges before executing user-controlled code.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• Windows 10/11 VM with a vulnerable Brother driver installer.
• Attacker with local user account (non-admin).
• Tools: Process Monitor (Procmon), PowerShell, Metasploit (for post-exploitation).

Exploitation Steps (Hypothetical):

1. Identify the vulnerable installer: Use Procmon to monitor file and registry operations during installation.
2. Create a malicious DLL: Write a DLL that spawns a reverse shell or adds a user to the Administrators group.
3. Exploit DLL Hijacking: Place the malicious DLL in a directory that the installer loads from (e.g., %TEMP% or %PUBLIC%).
4. Trigger the installer: Run the Brother driver installer. The malicious DLL is loaded with SYSTEM privileges.
5. Escalate: The attacker gains a shell with administrative rights.

Example PowerShell script to create a malicious DLL (for educational purposes only):

# Compile a DLL that adds a user to Administrators
Add-Type -TypeDefinition @"
using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
public class Exploit {
    [DllImport("kernel32.dll")]
    public static extern IntPtr GetProcAddress(IntPtr hModule, string procName);
    [DllImport("kernel32.dll")]
    public static extern IntPtr LoadLibrary(string lpFileName);
    public static void Main() {
        Process.Start("cmd.exe", "/c net localgroup Administrators attacker /add");
    }
}
"@ -OutputAssembly "malicious.dll"

Blue Team (Defensive)

Detection Steps:

1. Monitor for unusual DLL loads: Use Sysmon to log DLL load events (Event ID 7). Look for DLLs loaded from user-writable paths (e.g., C:\Users\*\AppData\Local\Temp\).
2. Check for symbolic link creation: Monitor for NtCreateSymbolicLinkObject calls (Sysmon Event ID 13).
3. Audit installer behavior: Run Brother installer in a sandboxed environment and analyze its file operations.
4. Harden the system: Apply the principle of least privilege. Ensure users do not have write access to directories used by installers.

Hunting Query (KQL for Microsoft Defender):

DeviceEvents
| where ActionType == "DllLoaded"
| where FileName endswith ".dll"
| where FolderPath startswith @"C:\Users\"
| where FolderPath contains @"\Temp\"
| where InitiatingProcessFileName contains "setup" or InitiatingProcessFileName contains "install"

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Placeholder – actual hashes unknown)
  • malicious.dll: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Process Names: setup.exe, brother_installer.exe
• Registry Keys: HKLM\SOFTWARE\Brother\ (modified by installer)
• Network Connections: Outbound connections to attacker C2 (e.g., 192.168.1.100:4444)
• File Paths: C:\Users\*\AppData\Local\Temp\*.dll, C:\Users\Public\*.dll

Detection Engineering

YARA Rule

rule CVE_2025_49797_Brother_PrivEsc {
    meta:
        description = "Detects malicious DLLs targeting Brother driver installer privilege escalation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-49797"
    strings:
        $s1 = "net localgroup Administrators" ascii wide nocase
        $s2 = "Add-Type" ascii wide nocase
        $s3 = "LoadLibrary" ascii wide nocase
        $s4 = "GetProcAddress" ascii wide nocase
    condition:
        any of ($s*) and filesize < 100KB
}

Sigma Rule

title: Brother Driver Installer Privilege Escalation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects suspicious DLL loads from user-writable paths during Brother driver installation
author: Valters IT
date: 2025-04-10
logsource:
    product: windows
    service: sysmon
detection:
    selection:
        EventID: 7
        Image|endswith: '\setup.exe'
        ImageLoaded|contains:
            - '\Temp\'
            - '\Public\'
    condition: selection
falsepositives:
    - Legitimate temporary files from other software
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2025-49797 Brother Driver Installer C2 Beacon"; flow:to_server,established; content:"|POST|"; http_method; content:"/beacon"; http_uri; classtype:trojan-activity; sid:1000001; rev:1;)

Remediation & Mitigation

1. Apply Vendor Patch: Check Brother’s official website for updated drivers. If a patch is available, install it immediately.
2. Restrict Local Access: Limit user accounts to standard privileges. Use Group Policy to prevent users from writing to %TEMP% or %PUBLIC% directories.
3. Enable AppLocker or WDAC: Block execution of unsigned DLLs from user-writable paths.
4. Monitor Installations: Use Sysmon and EDR solutions to monitor for suspicious behavior during driver installations.
5. Use Least Privilege: Run installer as a standard user if possible, or use a dedicated admin account for installations.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert