CVE-2021-42013

Apache HTTP Server contains a path traversal flaw (CWE-22) that can lead to remote code execution; CVE-2021-42013 resolves an incomplete patch previously issued for CVE-2021-41773. The flaw is triggered when files outside directories mapped by Alias-like directives are not protected by the default 'require all denied' configuration, or when CGI scripts are enabled, allowing an attacker to traverse outside the intended directory roots. An attacker can read files outside the configured paths, and where CGI script execution is enabled, achieve remote code execution on the server. The affected product per CISA is Apache HTTP Server; the source data does not specify exact version ranges, so defenders should consult the vendor advisory for fixed releases. Exploitation is confirmed in the wild: the vulnerability was added to CISA KEV on 2021-11-03 with known ransomware use, EPSS estimates a 100% probability of exploitation within 30 days, and no public PoC is listed.

What to do: Apply the Apache HTTP Server update per vendor instructions immediately, since this is a CISA KEV item with known ransomware use and near-certain near-term exploitation. Until patched, ensure directories targeted by Alias-like directives are covered by 'require all denied' defaults and disable CGI script execution where it is not required. Review access logs for path traversal probes and confirm no replaced version retains the incomplete earlier patch.