CVE-2024-43394: 
Apache HTTP Server vulnerability analysis and mitigation

Server-Side Request Forgery (SSRF) vulnerability in Apache HTTP Server on Windows allows potential leakage of NTLM hashes to a malicious server via modrewrite or apache expressions that pass unvalidated request input. The vulnerability affects Apache HTTP Server versions 2.4.0 through 2.4.63. The Apache HTTP Server Project has noted they will be implementing stricter criteria for accepting SSRF vulnerability reports regarding UNC paths, as the server provides limited protection against administrators directing the server to open UNC paths ([Apache Security](https://httpd.apache.org/security/vulnerabilities24.html)).

The vulnerability is classified as a Server-Side Request Forgery (SSRF) attack specifically targeting Windows-based Apache HTTP Server installations. The issue stems from improper validation of request input in mod_rewrite and apache expressions, which can be exploited to leak NTLM authentication hashes. The vulnerability has been assigned a CVSS v3.1 base score of 7.5 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N, indicating network accessibility with low attack complexity and no required privileges or user interaction (NVD Database).

The primary impact of this vulnerability is the potential exposure of NTLM authentication hashes to malicious servers. Windows servers are particularly vulnerable due to the nature of NTLM authentication when connecting over SMB. This could lead to unauthorized access if the captured NTLM hashes are successfully cracked or used in relay attacks (Apache Security).

The vulnerability has been patched in Apache HTTP Server version 2.4.64. As a workaround, Windows servers should implement restrictions on which hosts they will connect to via SMB, considering the nature of NTLM authentication. Organizations are strongly recommended to upgrade to version 2.4.64 to address this security issue (Apache Security).

The vulnerability was discovered and reported by Kainan Zhang (@4xpl0r3r) from Fortinet, highlighting the ongoing security research efforts in identifying potential SSRF vulnerabilities in widely-used web server software (Apache Security).