CVE-2025-40807 is a vulnerability classified under CWE-294 (Authentication Bypass) affecting Siemens Gridscale X Prepay versions earlier than 4.2.1. The flaw arises from the application's failure to properly protect authentication tokens against capture and replay attacks. An attacker who has previously authenticated—even if the user account is subsequently locked out—can capture valid authentication tokens and replay them to establish new sessions without re-authenticating. This bypasses the intended lockout mechanism, potentially allowing unauthorized access to the system. The vulnerability is exploitable remotely over the network (AV:N) with low attack complexity (AC:L), requiring low privileges (PR:L) but no user interaction (UI:N). The scope is unchanged (S:U), and the impact affects confidentiality, integrity, and availability to a limited extent (C:L/I:L/A:L). No public exploits have been reported yet, and Siemens has not released a patch at the time of publication. The vulnerability poses a risk to environments relying on Gridscale X Prepay for critical operations, as unauthorized session establishment could lead to data exposure or manipulation and service disruption. The lack of user interaction and low complexity make exploitation feasible for attackers with some level of access, emphasizing the need for prompt mitigation.

For European organizations, particularly those in the energy and industrial sectors where Siemens Gridscale X Prepay is deployed, this vulnerability could allow attackers to bypass authentication controls and maintain unauthorized access despite account lockouts. This undermines security policies designed to prevent brute force or compromised account misuse. The potential impact includes unauthorized data access, manipulation of prepaid energy management functions, and disruption of service availability. Although the confidentiality, integrity, and availability impacts are rated low to medium, the ability to bypass lockout mechanisms can facilitate persistent unauthorized access, increasing the risk of further exploitation or lateral movement within networks. Organizations operating critical infrastructure in Europe could face operational disruptions or regulatory compliance issues if this vulnerability is exploited. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially given the medium CVSS score and the critical nature of affected systems.

European organizations should implement the following specific mitigations: 1) Immediately restrict network access to Siemens Gridscale X Prepay interfaces to trusted IP ranges and enforce strict firewall rules to limit exposure. 2) Monitor authentication logs and session creation events for anomalies indicative of token replay, such as multiple sessions from the same token or sessions established after account lockout. 3) Enforce multi-factor authentication (MFA) where possible to add an additional layer of verification beyond tokens. 4) Segregate the Gridscale X Prepay environment from other critical network segments to reduce lateral movement risk. 5) Coordinate with Siemens for timely updates and apply patches as soon as version 4.2.1 or later is available. 6) Educate users and administrators about the risk of token capture and replay, emphasizing secure handling of authentication credentials. 7) Consider deploying network intrusion detection systems (NIDS) tuned to detect replay attack patterns. These measures go beyond generic advice by focusing on network-level controls, monitoring, and user behavior to mitigate the specific token replay vector.