CVE-2021-41773: Path Traversal in Apache HTTP Server 2.4.49

CVE-2021-41773 describes a flaw in path normalization introduced in Apache HTTP Server 2.4.49. An attacker can exploit path traversal to map URLs to files outside protected directories configured by Alias-like directives. If these files are not protected by the default 'require all denied' configuration and CGI scripts are enabled on these paths, remote code execution (RCE) is possible.

The vulnerability has a CVSS score of 9.8, classified as Critical. According to the official NVD description, exploitation is confirmed actively in the wild. Critically, the fix provided in Apache 2.4.50 was found to be incomplete, referencing a second advisory (CVE-2021-42013). This patch incompleteness demonstrates the flaw's complexity and the risk that administrators upgrading to 2.4.50 without further verification could remain vulnerable.

Administrators running Apache 2.4.49 must update immediately to a later version. It is essential to verify that the specific version you intend to adopt fully addresses the flaw by consulting CVE-2021-42013. In the interim, verify your Apache version, check if CGI is enabled on aliased paths, and ensure 'require all denied' is configured for directories outside configured Alias paths. Research on public repositories reveals technical analysis materials and practical labs still studying this flaw, a signal that it remains an attractive target for malicious actors.