Httpd 2.4.18 Exploit | Apache

Severity: 7.5 (High)
Type: Memory Information Leak (leading to RCE in some cases)

The Vulnerability:
CVE-2017-9798, discovered by Hanno Böck, was a use-after-free vulnerability in mod_http2. When Apache 2.4.18 was compiled with HTTP/2 support (not default in 2.4.18, but common), an attacker could trigger a memory leak. The leak disclosed the contents of the server’s memory, potentially including htaccess directives, private keys, or session data.

Why this matters for exploits:
While not a direct RCE, memory leaks can bypass ASLR (Address Space Layout Randomization), making it easier to chain with other exploits. In 2017, researchers demonstrated that by triggering OptionsBleed repeatedly, one could reconstruct HTTP/2 connection memory.

Check for vulnerability:

nmap --script http-apache-negotiation -p 80 target.com

The Exploit Code:
Public PoCs exist (e.g., optionsbleed.py). However, the exploit is reliable only on non-default builds:

Verdict: The closest to a high-impact exploit for 2.4.18, but limited by HTTP/2 activation.

  • Typical exploit types observed or feasible against unpatched 2.4.18 deployments:
  • Factors that increase exploitability:

    • Report ID: INFOSEC-APR-2026-01 Date: April 23, 2026 Subject: Vulnerability assessment of Apache HTTP Server version 2.4.18 apache httpd 2.4.18 exploit

    | Action | Command / Configuration | |--------|--------------------------| | Upgrade Apache | sudo apt-get upgrade apache2 (or compile 2.4.58+) | | Disable HTTP/2 | Protocols http/1.1 in httpd.conf | | Remove mod_cgi/cgid | sudo a2dismod cgi cgid | | Set ProxyRequest Off | Prevents HTTPOXY (Not a complete fix) | | Deploy WAF rule | Block Proxy header containing http:// or Proxy: * |

    | Attribute | Value | |-----------|-------| | Release Date | December 2015 | | HTTP/2 Support | Experimental (known bugs) | | End-of-Life Status | Officially EOL as of 2017 (unsupported) | | Common Distributions | Ubuntu 16.04 LTS (Xenial), Debian 9 (Stretch), RHEL 7.x (backported patches) |

    Note: Some Linux distributions backport security fixes. Always verify dpkg -l | grep apache2 or rpm -qa | grep httpd. A self-compiled 2.4.18 is the most dangerous scenario. Severity: 7

    The following CVEs have public proof-of-concept (PoC) exploits effective against unpatched 2.4.18.

    Exploitation of this vulnerability typically involves making HTTP requests to the server with headers or request methods that are specifically crafted to trigger the vulnerability. The goal is often to gain access to data that should not be accessible, potentially leading to information disclosure.