Apache Httpd 2.4.18 Exploit ◉ [Top]

The Hunt for Apache httpd 2.4.18 Exploits: A Retrospective on Vulnerabilities, Failures, and Mitigations

Introduction

In the world of web server security, version numbers often become shorthand for critical vulnerabilities. For system administrators and penetration testers, Apache HTTP Server 2.4.18 holds a particular, albeit complex, place in the collective memory. Released in December 2015, this version was the standard on several long-term support (LTS) Linux distributions, most notably Ubuntu 16.04 LTS (Xenial Xerus).

The Flaw: The server failed to limit the number of simultaneous stream workers for a single HTTP/2 connection. apache httpd 2.4.18 exploit

4. Public Exploit Availability (as of 2026)

| Platform | Exploit Type | Availability | |----------|--------------|---------------| | Metasploit Framework | Auxiliary/Scanner/http/httpoxy | ✅ Yes | | Exploit-DB | DoS via CVE-2017-9798 | ✅ EDB ID 42655 | | Shodan | Direct detection of 2.4.18 banner | ✅ High-fidelity | | Nuclei Templates | Custom risk scoring | ✅ Community templates | The Hunt for Apache httpd 2

During a "graceful" restart (apache2ctl graceful), the main process accesses this SHM to relocate "buckets." False positives (tools misreading version strings)

How it works: Apache 2.4.18 incorrectly trusts a user-supplied Proxy header and uses it to set the HTTP_PROXY environment variable for CGI-like scripts.

Mitigation: Disable HTTP/2 by removing h2 and h2c from the configuration or upgrade. X.509 Certificate Bypass

Title: "Exploiting Apache httpd 2.4.18: A Deep Dive into the Vulnerability and its Consequences"

  1. Upgrade to Apache HTTP Server 2.4.20 or later: The Apache HTTP Server project released version 2.4.20, which includes a fix for this vulnerability.
  2. Disable mod_http2: Disabling the mod_http2 module can prevent exploitation, but this may impact HTTP/2 protocol support.
  3. Apply patches: Backporting patches from later versions of Apache HTTP Server can also mitigate the vulnerability.