CVE-2025-27451: Endress Meac300 Auth Bypass Vulnerability

CVE-2025-27451 Overview

CVE-2025-27451 is a username enumeration vulnerability affecting the Endress MEAC300-FNADE4 emissions monitoring appliance and its firmware. The application returns distinct error messages during failed login attempts, differentiating between an incorrect password and a non-existent username. Attackers can iterate through candidate usernames and observe the response variation to build a list of valid accounts. This weakness is tracked under CWE-204 (Observable Response Discrepancy) and CWE-203 (Observable Discrepancy). The issue is network-exploitable without authentication or user interaction, though it discloses only account existence rather than credentials or system data.

Critical Impact
Unauthenticated remote attackers can enumerate valid usernames on the MEAC300-FNADE4 device, enabling targeted credential attacks against confirmed accounts.

Affected Products

Endress MEAC300-FNADE4 (hardware appliance)
Endress MEAC300-FNADE4 Firmware (all versions listed in the vendor advisory)
Emissions monitoring deployments integrating the MEAC300-FNADE4 platform

Discovery Timeline

2025-07-03 - CVE-2025-27451 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-27451

Vulnerability Analysis

The MEAC300-FNADE4 login interface returns different error responses depending on the failure condition. When a submitted username does not exist, the response differs from the response returned when the username exists but the password is wrong. Attackers script large username lists against the login endpoint and classify responses to identify valid accounts. The vulnerability itself does not grant access, but it removes a defensive layer that forces attackers to guess both the username and password simultaneously.

Once valid usernames are confirmed, attackers focus password-spraying, brute-force, or phishing campaigns on those accounts. In industrial control system (ICS) environments, where accounts often map to operators, engineers, or service technicians, enumeration accelerates targeted follow-on attacks.

Root Cause

The root cause is inconsistent error handling in the authentication workflow. The application executes username validation and password validation as separate stages and exposes the outcome of each stage through response content, status codes, or timing. Secure authentication design requires a single, uniform failure response regardless of which credential component is invalid.

Attack Vector

Exploitation requires only network reachability to the device's login interface. An attacker submits authentication requests with varying usernames and a fixed password, then compares the returned messages. The technique can be automated with common HTTP tooling and does not require prior credentials, elevated privileges, or user interaction on the target.

No public proof-of-concept has been published, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-27451

Indicators of Compromise

Repeated HTTP POST requests to the MEAC300-FNADE4 login endpoint originating from a single source with sequentially varying username parameters.
Elevated volumes of failed login events accompanied by distinct response patterns across attempted accounts.
Login attempts referencing usernames that do not exist in the local account database, indicating dictionary-based enumeration.

Detection Strategies

Correlate authentication logs from the MEAC300-FNADE4 device to identify high-frequency, low-success login patterns from individual source addresses.
Deploy network monitoring rules that flag repeated authentication requests with response-size or response-code variations to the device's management interface.
Baseline normal operator login behavior and alert on deviations such as after-hours access attempts or requests from unexpected network segments.

Monitoring Recommendations

Forward device authentication and web server logs to a centralized SIEM for long-window analysis and cross-source correlation.
Monitor the SICK PSIRT advisory page and the SICK CSAF advisory SCA-2025-0008 for firmware updates and additional detection guidance.
Track outbound reconnaissance behavior from ICS network zones that could indicate lateral movement following successful enumeration.

How to Mitigate CVE-2025-27451

Immediate Actions Required

Restrict network access to the MEAC300-FNADE4 management interface using firewall rules, VLAN segmentation, and jump-host access aligned with CISA ICS Recommended Practices.
Enforce rate limiting and account lockout on the authentication endpoint to slow automated enumeration attempts.
Review existing account inventories, disable unused accounts, and rotate credentials for privileged operator and service accounts.

Patch Information

Refer to the vendor advisory published as SICK CSAF SCA-2025-0008 (PDF) and SCA-2025-0008 (JSON) for firmware remediation details and fixed version information. Apply the vendor-supplied firmware update to the MEAC300-FNADE4 as soon as it is validated in your environment.

Workarounds

Place the device behind a reverse proxy or authenticating gateway that returns a uniform error response for all failed logins.
Limit login interface exposure to a dedicated engineering workstation subnet and block direct access from general IT or external networks.
Enable multi-factor authentication on upstream access mechanisms so that username enumeration alone provides limited value to an attacker.

bash

# Example firewall restriction limiting MEAC300-FNADE4 management access to an engineering subnet
iptables -A INPUT -p tcp --dport 443 -s 10.20.30.0/24 -d <device_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -d <device_ip> -j DROP