CVE-2024-43394 is a Server-Side Request Forgery (SSRF) vulnerability classified under CWE-918, affecting Apache HTTP Server versions 2.4.0 through 2.4.63 on Windows platforms. The vulnerability stems from the server's handling of unvalidated request inputs passed through mod_rewrite rules or Apache expressions that can reference UNC (Universal Naming Convention) paths. When exploited, the server can be tricked into initiating SMB (Server Message Block) connections to attacker-controlled hosts. This behavior can cause the server to send NTLM (NT LAN Manager) authentication hashes to the malicious SMB server, potentially allowing attackers to capture these hashes for offline cracking or relay attacks. The issue arises because the Apache HTTP Server offers limited protection against administrators configuring the server to open UNC paths, and Windows servers inherently use NTLM authentication over SMB. The vulnerability does not require any privileges or user interaction and can be triggered remotely, making it a significant risk. Although no public exploits have been reported yet, the potential for credential leakage and subsequent lateral movement or privilege escalation is high. The Apache Software Foundation has indicated a forthcoming increase in the scrutiny of SSRF reports involving UNC paths, suggesting ongoing efforts to harden this attack surface. The CVSS v3.1 score of 7.5 reflects a network attack vector with low complexity, no privileges required, no user interaction, and a high impact on confidentiality but no impact on integrity or availability.

For European organizations, this vulnerability poses a substantial risk to confidentiality, particularly for those running Apache HTTP Server on Windows environments. The leakage of NTLM hashes can lead to credential compromise, enabling attackers to perform lateral movement within corporate networks or escalate privileges. Critical sectors such as finance, government, healthcare, and energy, which often rely on Windows-based infrastructure and Apache HTTP Server, could face targeted attacks exploiting this vulnerability. The exposure of NTLM hashes also increases the risk of man-in-the-middle or relay attacks, potentially undermining trust in internal authentication mechanisms. Given the widespread use of Apache HTTP Server in Europe and the common deployment of Windows servers in enterprise environments, the vulnerability could facilitate espionage, data breaches, and disruption of services. The lack of known exploits currently provides a window for proactive mitigation, but the ease of exploitation and high confidentiality impact necessitate urgent attention.

European organizations should immediately audit their Apache HTTP Server deployments on Windows to identify affected versions (2.4.0 through 2.4.63). Since no official patches are listed yet, organizations should implement the following mitigations: (1) Restrict SMB outbound connections from Apache servers to only trusted hosts using firewall rules or network segmentation to prevent unauthorized SMB communication. (2) Review and sanitize all mod_rewrite rules and Apache expressions to ensure they do not accept unvalidated user input that could reference UNC paths. (3) Disable or limit the use of UNC paths in server configurations where possible. (4) Monitor network traffic for unusual SMB connection attempts originating from Apache servers. (5) Employ network intrusion detection systems (NIDS) with signatures for SSRF and SMB relay attempts. (6) Plan for timely patching once Apache releases an official fix. (7) Educate system administrators about the risks of SSRF via UNC paths and the importance of secure configuration. These steps go beyond generic advice by focusing on network-level controls and configuration hygiene specific to this vulnerability.