CVE-2025-27451 is a medium-severity vulnerability identified in the Endress+Hauser MEAC300-FNADE4 product. The vulnerability arises from an observable response discrepancy during failed login attempts. Specifically, the application returns distinct error messages depending on whether the login failure was due to an incorrect password or a non-existent username. This behavior constitutes a CWE-204 (Observable Response Discrepancy) weakness, which can be exploited by an attacker to enumerate valid usernames on the system. By systematically submitting login attempts with different usernames and analyzing the error messages, an attacker can confirm which usernames exist, facilitating further targeted attacks such as brute force password guessing or social engineering. The vulnerability has a CVSS v3.1 base score of 5.3, reflecting a network attack vector with low attack complexity, no privileges or user interaction required, and limited confidentiality impact. There is no indication of known exploits in the wild, and no patches have been linked yet. The affected version is listed as '0', which likely indicates the initial or current version of the product at the time of disclosure. The vulnerability does not impact integrity or availability directly but leaks information that can aid attackers in reconnaissance and subsequent attack phases.

For European organizations using the Endress+Hauser MEAC300-FNADE4 device, this vulnerability primarily poses an information disclosure risk that can facilitate further attacks. The ability to enumerate valid usernames can lead to targeted brute force or credential stuffing attacks, increasing the risk of unauthorized access. Given that Endress+Hauser products are commonly used in industrial automation and process control environments, exploitation could indirectly impact operational technology (OT) environments if attackers gain access through compromised credentials. This could lead to operational disruptions, safety risks, or data breaches. The confidentiality impact is limited to username disclosure; however, the strategic importance of these devices in critical infrastructure sectors such as manufacturing, energy, and utilities in Europe elevates the potential consequences of chained attacks. Organizations in these sectors must be vigilant, as attackers often leverage such reconnaissance vulnerabilities as initial footholds. The lack of required authentication or user interaction lowers the barrier for exploitation, increasing the likelihood of automated scanning and enumeration attempts.

To mitigate this vulnerability, organizations should implement uniform error messages for all failed login attempts, ensuring that responses do not reveal whether a username exists. This can be achieved by standardizing authentication failure messages to a generic text such as 'Invalid username or password.' Additionally, implementing account lockout or throttling mechanisms after a defined number of failed login attempts can reduce the risk of automated username enumeration and brute force attacks. Network-level protections such as Web Application Firewalls (WAFs) or Intrusion Detection/Prevention Systems (IDS/IPS) should be configured to detect and block suspicious login patterns indicative of enumeration attempts. Organizations should also monitor authentication logs for unusual activity and consider multi-factor authentication (MFA) where feasible to add an additional security layer. Since no patches are currently available, these compensating controls are critical. Finally, organizations should engage with Endress+Hauser for updates and apply patches promptly once released.