CVE-2025-54090 is a vulnerability identified in the Apache HTTP Server version 2.4.64, specifically related to the handling of the "RewriteCond expr ..." directive within the server's URL rewriting module. The flaw stems from an incorrect check of a function's return value (classified under CWE-253), which causes all conditional expressions evaluated by "RewriteCond expr ..." to incorrectly return true regardless of their actual logic. This means that any conditional rewrite rules relying on this expression evaluation will be bypassed or misapplied, potentially leading to unintended URL rewriting behavior. Such behavior can undermine security controls implemented through rewrite rules, including access restrictions, redirections, or other conditional logic intended to protect resources or enforce policies. The vulnerability does not require authentication or user interaction to be triggered, as it is inherent in the server's processing of rewrite conditions. Although no known exploits are reported in the wild yet, the flaw's nature suggests it could be leveraged by attackers to bypass security policies or access controls configured via rewrite rules. The Apache Software Foundation has addressed this issue in version 2.4.65, and users are strongly advised to upgrade to this version to mitigate the risk.

For European organizations, the impact of CVE-2025-54090 can be significant, especially for those relying heavily on Apache HTTP Server 2.4.64 for web hosting and application delivery. Misconfigured or maliciously exploited rewrite rules could allow attackers to bypass access controls, redirect users to malicious sites, or expose sensitive internal resources unintentionally. This could lead to data leakage, unauthorized access, or facilitate further attacks such as phishing or malware distribution. Given Apache HTTP Server's widespread use across European enterprises, government agencies, and service providers, the vulnerability could affect a broad range of sectors including finance, healthcare, public administration, and e-commerce. The absence of authentication or user interaction requirements increases the risk of automated exploitation attempts. Additionally, the flaw could undermine compliance with data protection regulations like GDPR if unauthorized data access occurs due to bypassed controls.

European organizations should prioritize upgrading Apache HTTP Server instances from version 2.4.64 to 2.4.65 or later immediately to remediate this vulnerability. Beyond patching, administrators should audit all rewrite rules using "RewriteCond expr ..." directives to verify their logic and ensure they are not relying on the flawed behavior. Implementing additional layers of access control at the application or network level can reduce reliance on rewrite rules for security enforcement. Monitoring web server logs for unusual rewrite behavior or unexpected access patterns can help detect exploitation attempts. Organizations should also review their incident response plans to include scenarios involving web server misconfigurations or bypasses. For environments where immediate patching is not feasible, temporarily disabling or restricting the use of "RewriteCond expr ..." directives may reduce exposure. Finally, maintaining an up-to-date inventory of Apache HTTP Server versions deployed across infrastructure will facilitate rapid identification and remediation of vulnerable instances.