CVE-2025-27459: Meac300-fnade4 Information Disclosure Flaw

CVE-2025-27459 Overview

CVE-2025-27459 is a cryptographic vulnerability affecting the Endress MEAC300-FNADE4 firmware, where the embedded VNC application stores its passwords encrypted within the Windows registry using the Data Encryption Standard (DES) algorithm. DES is a legacy encryption algorithm that has been considered cryptographically broken since the late 1990s due to its short 56-bit key length, which makes it susceptible to brute-force attacks with modern computing resources. An attacker with access to the registry can recover the original VNC passwords, potentially gaining unauthorized remote access to affected industrial control systems.

Critical Impact

Attackers can recover plaintext VNC credentials from registry storage, enabling unauthorized remote access to industrial control systems without authentication barriers.

Affected Products

• Endress MEAC300-FNADE4 Firmware (all versions)
• Endress MEAC300-FNADE4 Hardware Device

Discovery Timeline

• 2025-07-03 - CVE-2025-27459 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2025-27459

Vulnerability Analysis

This vulnerability falls under CWE-257 (Storing Passwords in a Recoverable Format), which occurs when credentials are stored using reversible encryption methods that allow recovery of the original plaintext. The fundamental issue is the use of DES encryption for protecting VNC authentication credentials stored in the Windows registry.

DES was designed in the 1970s and uses a 56-bit key length, which can be exhaustively searched in a matter of hours using modern hardware such as GPUs or FPGAs. Furthermore, the standard VNC implementation uses a well-known hardcoded key for DES encryption, making the decryption process even more trivial for attackers who understand this implementation detail.

The vulnerability enables network-based exploitation without requiring user interaction or prior authentication. An attacker who can read the registry values—either through local access, lateral movement, or remote registry enumeration—can decrypt the VNC password and use it to establish a remote desktop session to the affected industrial device.

Root Cause

The root cause of this vulnerability is the use of the obsolete DES encryption algorithm for storing VNC passwords in the Windows registry. VNC implementations historically use a fixed, publicly-known 8-byte key for DES encryption, which means the encryption provides only obscurity rather than true cryptographic protection. The design decision to use DES dates back to early VNC implementations and has never been updated in this firmware to use modern encryption standards such as AES-256.

Attack Vector

The attack vector is network-based, as indicated by the AV:N designation in the CVSS vector. An attacker can exploit this vulnerability through the following attack chain:

1. Registry Access: The attacker gains read access to the Windows registry on the target device, either through local access, remote registry enumeration, or by compromising a backup that contains registry hives
2. Password Extraction: The encrypted VNC password is extracted from registry keys typically located at HKEY_LOCAL_MACHINE\SOFTWARE\RealVNC or similar paths depending on the VNC implementation
3. DES Decryption: Using readily available tools or scripts, the attacker decrypts the password using the known VNC DES key
4. Remote Access: The recovered plaintext password is used to authenticate to the VNC server running on the industrial control device

The exploitation is straightforward because the DES key used by VNC is well-documented in security research, and multiple open-source tools exist specifically for recovering VNC passwords from registry entries.

Detection Methods for CVE-2025-27459

Indicators of Compromise

• Unusual remote registry access attempts targeting VNC-related registry keys
• Multiple failed VNC authentication attempts followed by a successful login
• VNC connections from unexpected IP addresses or geographic locations
• Registry query events targeting HKEY_LOCAL_MACHINE\SOFTWARE\RealVNC or equivalent paths
• Presence of VNC password decryption tools on systems within the network

Detection Strategies

• Monitor Windows Security Event Logs for remote registry access events (Event ID 4663) targeting VNC registry paths
• Deploy network intrusion detection rules to identify VNC protocol traffic from unauthorized source addresses
• Implement file integrity monitoring on registry hives to detect unauthorized access attempts
• Use endpoint detection and response (EDR) solutions to identify execution of known VNC password recovery tools

Monitoring Recommendations

• Enable detailed auditing on registry keys containing VNC credentials
• Configure SIEM alerts for patterns consistent with credential extraction activities
• Monitor network traffic for VNC connections (default port 5900) to industrial control systems
• Review authentication logs on affected devices for anomalous remote access patterns

How to Mitigate CVE-2025-27459

Immediate Actions Required

• Restrict network access to affected Endress MEAC300-FNADE4 devices using firewall rules and network segmentation
• Disable VNC remote access if not operationally required
• Change VNC passwords immediately and implement additional authentication layers
• Monitor for unauthorized access attempts to affected systems
• Review the SICK CSAF Advisory for vendor-specific guidance

Patch Information

Organizations should consult the SICK PSIRT page and Endress Product Security resources for official firmware updates addressing this vulnerability. Until a patch is available, compensating controls should be implemented to reduce exposure.

Additionally, organizations operating industrial control systems should review the CISA ICS Recommended Practices for comprehensive guidance on securing operational technology environments.

Workarounds

• Implement network segmentation to isolate affected devices from untrusted networks and limit VNC access to authorized management stations only
• Use VPN tunnels or SSH tunneling to encrypt VNC traffic and add an additional authentication layer
• Configure host-based firewalls on affected devices to restrict VNC connections to specific IP addresses
• Consider replacing VNC with more secure remote access solutions that use modern encryption standards
• Implement multi-factor authentication (MFA) at the network perimeter for any remote access to industrial control systems

# Example: Restrict VNC access using Windows Firewall (PowerShell)
# Block all inbound VNC connections except from trusted management subnet
New-NetFirewallRule -DisplayName "Block VNC Inbound" -Direction Inbound -LocalPort 5900 -Protocol TCP -Action Block
New-NetFirewallRule -DisplayName "Allow VNC from Management" -Direction Inbound -LocalPort 5900 -Protocol TCP -RemoteAddress 10.0.100.0/24 -Action Allow