Path Traversal & Remote Code Execution in Apache HTTP Server (CVE‑2021‑41773)

Path Traversal & Remote Code Execution in Apache HTTP Server (CVE‑2021‑41773)

What It Is – Apache HTTP Server 2.4.49 and earlier allow a crafted URL to traverse directories outside the intended document root. When combined with mis‑configured Alias directives or enabled CGI scripts, an attacker can achieve remote code execution (RCE).

Exploitability – Public exploits and proof‑of‑concept code have been circulating since the vulnerability’s disclosure. The CVSS v3.1 base score is 7.5 (High).

Affected Products – Apache HTTP Server 2.4.49 and earlier releases (all platforms).

Why It Matters for Trust & Control Assurance

• Configuration control – The flaw highlights the need for a documented, continuously‑monitored configuration baseline (access control to file paths, “require all denied” defaults).
• Patch management evidence – Demonstrating timely remediation is a core audit artifact for frameworks such as NIST CSF 2.0.
• Defensible audit trail – Logging of configuration changes and verification of CGI disablement provides the evidence auditors request when assessing “Secure Configuration Management” controls.

Recommended Actions

• Inventory all Apache HTTP Server instances and verify version numbers.
• Apply the official Apache patch (or upgrade to 2.4.51+). The patch for CVE‑2021‑41773 alone is insufficient; also apply the companion fix for CVE‑2021‑42013.
• Review all Alias and ScriptAlias directives; ensure Require all denied is the default for any directory not explicitly allowed.
• Disable CGI scripts unless absolutely required, and restrict execution permissions on the server file system.
• Run a configuration‑compliance scan and capture evidence of the hardened settings for audit readiness.

Source: CISA KEV – CVE‑2021‑41773