CVE-2025-27458: Endress Meac300 Info Disclosure Flaw

CVE-2025-27458 Overview

CVE-2025-27458 is a cryptographic vulnerability affecting the VNC authentication mechanism in Endress MEAC300-FNADE4 firmware. The vulnerability stems from the VNC authentication protocol's reliance on a challenge-response system where both server and client use the same password for encryption. The challenge is sent from the server to the client, encrypted by the client, and sent back. The server performs the same encryption locally and verifies the responses match to confirm the client knows the correct password.

Since all VNC communication is transmitted unencrypted, an attacker with network access can intercept the challenge and response traffic and attempt to derive the password from this captured information. This weakness in the authentication protocol exposes industrial control systems to credential theft and unauthorized access.

Critical Impact

Network-based attackers can capture VNC authentication traffic and perform offline password cracking attacks to gain unauthorized access to industrial control systems.

Affected Products

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

Discovery Timeline

• 2025-07-03 - CVE-2025-27458 published to NVD
• 2026-02-06 - Last updated in NVD database

Technical Details for CVE-2025-27458

Vulnerability Analysis

This vulnerability is classified under CWE-327 (Use of a Broken or Risky Cryptographic Algorithm). The fundamental issue lies in the design of the VNC authentication protocol itself, which transmits authentication challenges and responses over an unencrypted channel. When a client connects to a VNC server, the server sends a random 16-byte challenge. The client encrypts this challenge using DES with the password as the key and returns the encrypted response. The server performs the identical encryption and compares results.

The problem is twofold: first, the communication channel is not encrypted, allowing passive network eavesdropping; second, the DES encryption used has known weaknesses, including a limited 8-character password length and a 56-bit effective key size that makes brute-force attacks feasible with modern computing resources.

An attacker positioned on the same network segment as the target device can capture the challenge-response exchange and perform an offline dictionary or brute-force attack to recover the VNC password without any interaction with the target system.

Root Cause

The root cause of this vulnerability is the inherent design limitation of the RFB (Remote Framebuffer) protocol's VNC authentication scheme. The protocol was designed in an era when network security threats were less sophisticated and does not incorporate modern cryptographic best practices. Specifically:

• No transport layer encryption protects the authentication exchange
• The symmetric encryption algorithm (DES) used for password verification is cryptographically weak
• Password truncation to 8 characters limits entropy regardless of user-chosen password complexity

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker must have passive network access to intercept traffic between a VNC client and the Endress MEAC300-FNADE4 device. The attack sequence involves:

1. Positioning on the network to capture traffic (via ARP spoofing, network tap, or compromised network infrastructure)
2. Capturing the 16-byte challenge sent by the server
3. Capturing the encrypted response sent by the client
4. Performing offline password recovery using the captured challenge-response pair

The attacker can use tools designed for VNC password recovery that implement dictionary attacks or brute-force methods against the captured authentication data. Given the 8-character password limitation and DES encryption, even strong passwords can be recovered within reasonable timeframes.

Detection Methods for CVE-2025-27458

Indicators of Compromise

• Unusual network traffic patterns on VNC port 5900 or configured VNC ports to/from Endress devices
• ARP anomalies or gratuitous ARP packets indicating potential man-in-the-middle positioning
• Unexpected VNC connection attempts following periods of network reconnaissance
• Multiple failed VNC authentication attempts from previously unseen IP addresses
• Evidence of packet capture tools or network sniffing activity on industrial network segments

Detection Strategies

• Deploy network intrusion detection systems (NIDS) to monitor for unencrypted VNC traffic on industrial control networks
• Implement network flow analysis to identify VNC connections from unauthorized sources or network segments
• Configure alerts for VNC authentication failures combined with successful authentications from the same or different source IPs
• Monitor for ARP spoofing or other network layer attacks that could facilitate traffic interception

Monitoring Recommendations

• Establish baseline VNC connection patterns and alert on deviations from normal administrative access
• Implement deep packet inspection for VNC protocol analysis where feasible
• Deploy network segmentation monitoring to detect lateral movement attempts toward Endress devices
• Enable comprehensive logging on network infrastructure devices to capture evidence of traffic interception attempts
• Conduct periodic reviews of authorized VNC access sources and validate against observed connection patterns

How to Mitigate CVE-2025-27458

Immediate Actions Required

• Restrict VNC access to the Endress MEAC300-FNADE4 devices to trusted administrative workstations only
• Implement network segmentation to isolate industrial control systems from general network traffic
• Deploy VPN tunnels or SSH tunneling to encrypt VNC traffic between administrative workstations and affected devices
• Review and limit the IP addresses permitted to establish VNC connections to these devices
• Consider disabling VNC entirely if alternative remote management options are available

Patch Information

Consult the vendor security advisories for firmware updates that may address this vulnerability. The SICK PSIRT Overview page and the SICK CSAF White Paper (PDF) provide official guidance. Additionally, follow CISA ICS Recommended Practices for securing industrial control systems.

Workarounds

• Tunnel all VNC connections through an encrypted channel such as VPN or SSH port forwarding to prevent traffic interception
• Implement strict firewall rules permitting VNC access only from designated management stations
• Deploy a jump host or bastion server architecture requiring authenticated access before reaching VNC-enabled devices
• Use network access control (NAC) solutions to ensure only authorized devices can communicate with industrial systems
• Consider implementing additional authentication layers such as certificate-based VPN access before VNC connections are permitted

# Example SSH tunnel configuration for VNC traffic protection
# Run on administrative workstation to create encrypted tunnel
ssh -L 5901:meac300-device-ip:5900 jump-host-user@jump-host-ip

# Connect VNC client to localhost:5901 instead of direct device connection
# This encrypts all VNC traffic through the SSH tunnel