CVE-2021-41773

Apache HTTP Server contains a path traversal flaw (CWE-22) that lets crafted HTTP requests reach files outside directories configured via Alias-like directives. When files outside those aliased directories are not protected by the default 'require all denied' policy, attackers can read arbitrary files outside the intended root, and if CGI scripts are enabled the traversal can be escalated to remote code execution under the web server account. Anyone running an affected Apache HTTP Server release with such a configuration is exposed; the initial 2.4.50 patch was incomplete, so the flaw's full remediation is tracked under CVE-2021-42013. Exploitation is confirmed in the wild: CISA added the vulnerability to the KEV catalog on 2021-11-03 with known ransomware use, and EPSS assigns a ~100% probability of exploitation within 30 days (100th percentile).

What to do: Upgrade to Apache HTTP Server 2.4.51 or later; do not stop at 2.4.50, since its fix was incomplete (see CVE-2021-42013). As an interim mitigation, ensure directories referenced by Alias-like directives are covered by 'require all denied' and disable or restrict CGI (mod_cgi/mod_cgid) on traversable paths. Review access logs for traversal patterns such as /icons/../ and unexpected CGI invocations, and hunt for webshells or ransomware staging given the known ransomware use.