CVE-2024-43204 is a Server-Side Request Forgery (SSRF) vulnerability identified in the Apache HTTP Server maintained by the Apache Software Foundation. This vulnerability arises when the mod_proxy module is loaded alongside a specific mod_headers configuration that modifies the Content-Type header based on values provided in incoming HTTP requests. An attacker can exploit this by crafting HTTP requests that manipulate the Content-Type header, causing the server to send outbound proxy requests to URLs controlled by the attacker. This SSRF flaw can be leveraged to perform unauthorized internal network scanning, access internal services, or bypass firewall restrictions by making the server act as a proxy. The vulnerability affects Apache HTTP Server versions starting from 2.4.0 up to but not including 2.4.64, where the issue has been fixed. The CVSS v3.1 base score is 7.5, indicating a high severity due to the lack of required privileges or user interaction and the potential for integrity impact. However, exploitation requires an uncommon configuration involving mod_headers, which reduces the likelihood of widespread exploitation. No known public exploits or active attacks have been reported to date. The recommended mitigation is to upgrade to Apache HTTP Server version 2.4.64, which contains the patch addressing this SSRF vulnerability.

For European organizations, this vulnerability poses a significant risk primarily to the integrity of their web server operations. Exploitation could allow attackers to manipulate server-side requests, potentially accessing internal network resources, sensitive backend services, or restricted data not normally exposed externally. This could lead to unauthorized actions within the internal network, lateral movement, or reconnaissance activities that precede more severe attacks. While confidentiality and availability impacts are not directly indicated, the ability to send arbitrary requests could facilitate further exploitation chains. Organizations running Apache HTTP Server with mod_proxy and mod_headers configured to modify Content-Type headers are particularly vulnerable. Critical infrastructure, government services, financial institutions, and enterprises with complex proxy configurations are at heightened risk. The lack of authentication or user interaction required for exploitation increases the threat level. Prompt patching is essential to prevent attackers from leveraging this vulnerability in targeted attacks or automated scanning campaigns.

1. Upgrade Apache HTTP Server to version 2.4.64 or later immediately, as this version contains the official fix for CVE-2024-43204. 2. Review and audit server configurations to identify if mod_proxy and mod_headers are enabled and if mod_headers is configured to modify the Content-Type header based on user input; disable or restrict such configurations if possible. 3. Implement strict input validation and sanitization on HTTP headers to prevent injection of malicious values. 4. Employ network segmentation and firewall rules to limit outbound HTTP requests from web servers to only trusted destinations, reducing the impact of SSRF exploitation. 5. Monitor web server logs for unusual outbound requests or anomalies in Content-Type header usage that could indicate exploitation attempts. 6. Use Web Application Firewalls (WAFs) with rules designed to detect and block SSRF patterns, especially those targeting proxy modules. 7. Conduct internal penetration testing focusing on SSRF vectors to validate the effectiveness of mitigations and identify residual risks. 8. Educate system administrators and security teams about the specific configuration risks related to mod_headers and mod_proxy to prevent misconfigurations.