CVE-2025-54090 is a medium-severity vulnerability identified in Apache HTTP Server version 2.4.64. The issue stems from an incorrect check of a function's return value related to the "RewriteCond expr ..." directive, which is part of the mod_rewrite module used for URL rewriting. Specifically, due to this bug, all conditional expressions evaluated by "RewriteCond expr ..." are incorrectly treated as true, regardless of their actual logic or intended conditions. This behavior can lead to unintended URL rewriting rules being applied, potentially allowing attackers to bypass intended access controls, redirect users to malicious sites, or expose sensitive resources unintentionally. The vulnerability is classified under CWE-253 (Incorrect Check of Function Return Value), indicating a logic flaw in how the software validates the outcome of a function call. The CVSS v3.1 base score is 6.3, reflecting a medium severity with network attack vector, low attack complexity, requiring privileges (PR:L), no user interaction, and impacts on confidentiality, integrity, and availability. No known exploits are currently reported in the wild, and the issue was publicly disclosed on July 23, 2025. The recommended remediation is to upgrade Apache HTTP Server to version 2.4.65, where this bug has been fixed.

For European organizations, this vulnerability poses a significant risk primarily to those relying on Apache HTTP Server 2.4.64 with mod_rewrite rules that use the "RewriteCond expr ..." directive for access control or URL management. Misinterpretation of rewrite conditions can lead to unauthorized access to restricted resources, exposure of sensitive data, or redirection to malicious endpoints, potentially facilitating phishing or data exfiltration attacks. Given Apache HTTP Server's widespread use in web infrastructure across Europe, especially in government, financial, healthcare, and e-commerce sectors, exploitation could disrupt service availability and compromise data integrity and confidentiality. The requirement for privileges to exploit (PR:L) suggests that attackers would need some level of access to the server, which might limit remote exploitation but raises concerns about insider threats or attackers who have already compromised lower-privileged accounts. The absence of user interaction lowers the barrier for automated exploitation once privileges are obtained. Overall, the vulnerability could undermine trust in web services and lead to regulatory compliance issues under GDPR if personal data is exposed.

European organizations should prioritize upgrading all Apache HTTP Server instances from version 2.4.64 to 2.4.65 or later to ensure the vulnerability is patched. Beyond patching, administrators should audit all mod_rewrite configurations, especially those using "RewriteCond expr ..." directives, to verify that rewrite rules behave as intended and do not inadvertently grant access or redirect traffic improperly. Implement strict access controls to limit the number of users with privileges capable of modifying Apache configurations or executing code on the server. Employ monitoring and alerting on configuration changes and unusual rewrite rule evaluations. Additionally, consider deploying web application firewalls (WAFs) that can detect and block suspicious URL rewriting behaviors. Regularly review server logs for anomalies related to URL rewriting and access patterns. Finally, incorporate this vulnerability into incident response plans to rapidly address any exploitation attempts.