CVE‑2021‑40438: Apache HTTP Server SSRF Vulnerability Allows Remote Request Redirection
What It Is — A Server‑Side Request Forgery (SSRF) flaw in mod_proxy lets an attacker craft a URI‑path that forces the Apache HTTP Server to forward the request to an arbitrary origin chosen by the remote user.
Exploitability — Public proof‑of‑concept code exists; the vulnerability is rated CVSS 3.1 7.5 (HIGH) and can be exploited without authentication on vulnerable versions.
Affected Products — Apache HTTP Server 2.4.48 and all earlier releases.
Why It Matters for Trust & Control Assurance
- Continuous control monitoring – Detecting unauthorized outbound requests from web servers is a key control evidence point for any audit of network egress.
- Patch‑management diligence – Demonstrating that critical web‑infrastructure is kept up‑to‑date provides defensible proof of due‑diligence to regulators and enterprise buyers.
- Configuration audit trail – Maintaining a verifiable history of
mod_proxysettings supports a robust audit trail and reduces exposure to supply‑chain‑related attacks.
Recommended Actions
- Upgrade Apache HTTP Server to version 2.4.49 or later, where the SSRF issue is fixed.
- Review and harden
mod_proxyconfigurations; restrict allowed target hosts and enforce allow‑list rules. - Enable detailed logging of proxy requests and monitor for anomalous outbound connections.
- Validate that your continuous monitoring platform captures proxy‑related events as control evidence.
- Document the remediation steps in your change‑management system to provide audit‑ready evidence.
Source: CISA KEV – CVE‑2021‑40438