Apache Httpd 2.4.18 Exploit File

CVE-2016-6806: Apache HTTP Server 2.4.18 Vulnerability

In 2016, a critical vulnerability was discovered in the Apache HTTP Server version 2.4.18, which is a popular open-source web server software. The vulnerability, tracked as CVE-2016-6806, is a use-after-free vulnerability in the mod_http2 module.

Vulnerability Details

The vulnerability exists in the mod_http2 module, which provides HTTP/2 protocol support for the Apache HTTP Server. The flaw occurs when handling a specially crafted HTTP/2 request, which can lead to a use-after-free condition. This allows an attacker to potentially execute arbitrary code or cause a denial-of-service (DoS) attack.

Exploit Details

The exploit for this vulnerability involves sending a specially crafted HTTP/2 request to the vulnerable Apache HTTP Server. The request must contain a specific sequence of headers and body content that triggers the use-after-free condition. Successful exploitation can lead to:

  1. Remote Code Execution (RCE): An attacker can execute arbitrary code on the vulnerable system, potentially leading to a complete compromise of the system.
  2. Denial-of-Service (DoS): An attacker can cause the Apache HTTP Server to crash or become unresponsive, leading to a denial-of-service condition.

Proof-of-Concept (PoC) and Exploits

Several proof-of-concept (PoC) exploits and working exploits were released publicly, demonstrating the feasibility of the vulnerability. These exploits typically involve using tools like curl or custom scripts to send the specially crafted HTTP/2 requests to the vulnerable server.

Mitigation and Fixes

To mitigate this vulnerability, administrators can:

  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.

Paper and Resources

If you're looking for an in-depth paper on this topic, here are a few resources:

  • CVE-2016-6806: The official CVE page provides a summary of the vulnerability.
  • Apache HTTP Server 2.4.18 Vulnerability: A detailed write-up on the vulnerability and its exploitation by the Apache HTTP Server project.
  • Exploit-DB: A proof-of-concept exploit is available on Exploit-DB.

Keep in mind that publicly releasing exploits can be problematic, as it may put vulnerable systems at risk. Always prioritize responsible disclosure and follow best practices for vulnerability management.

Understanding the Risks of Apache httpd 2.4.18 Apache httpd version 2.4.18, released in late 2015, remains common in legacy environments—most notably as the default version in Ubuntu 16.04 LTS (Xenial Xerus)

. However, sticking with this version today poses significant security risks. If you are still running 2.4.18, you are exposed to several well-documented vulnerabilities that can lead to everything from information leaks to full server compromise. Key Vulnerabilities in Apache 2.4.18

While 2.4.18 was a stable release in its time, years of security research have uncovered critical flaws that affect it:

Trending CVEs for the Week of April 8th, 2019 - Blog - NopSec apache httpd 2.4.18 exploit

Apache HTTP Server 2.4.18, like any software, may have vulnerabilities that can be exploited by attackers. One notable vulnerability in Apache HTTP Server 2.4.18 is the "OptionsBleed" vulnerability, which is identified as CVE-2017-9798. This vulnerability allows an attacker to read sensitive data from the server's memory by making a specially crafted request.

Here is a basic guide to understanding and potentially mitigating this vulnerability:

Minimal exploitation example (conceptual)

  • Many DoS vectors rely on sending malformed chunked-encoded requests or large numbers of partial requests to exhaust worker threads or trigger parsing bugs; such tests should only be run on isolated lab systems.

3. The Real RCE Threat: CVE-2017-9798 (OptionsBleed)

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:

  • Apache 2.4.18 with --enable-http2 (rare in LTS distros)
  • Unpatched versions (fixed in Apache 2.4.28)

Verdict: The closest to a high-impact exploit for 2.4.18, but limited by HTTP/2 activation. CVE-2016-6806: Apache HTTP Server 2

Exploit Payload Example

An attacker targeting a 2.4.18 proxy setup might send:

POST / HTTP/1.1
Host: vulnerable-website.com
Content-Length: 50
Transfer-Encoding: chunked
Content-Length: 0

0


GET /admin/delete?user=admin HTTP/1.1
Host: vulnerable-website.com
Foo: x

Technical breakdown: The front-end proxy processes the Transfer-Encoding: chunked, sees the 0 chunk, and ends the request. But Apache 2.4.18 keeps the socket open and interprets the subsequent GET /admin... as a second request—originating from the victim’s IP, bypassing ACLs.

3.1 CVE-2016-5387 – "HTTPOXY"

  • Type: Man-in-the-middle / Proxy hijacking
  • Vector: HTTP_PROXY environment variable injection via Proxy: header
  • Impact: Attacker forces CGI scripts to route outgoing requests through a malicious proxy.
  • Public Exploit: httpoxy scanner tools, Metasploit auxiliary module.
  • Apache 2.4.18 status: Exploitable unless mod_cgi or mod_cgid is disabled.

3.3 CVE-2017-9798 – "Optionsbleed"

  • Type: Memory disclosure
  • Vector: OPTIONS * request with Limit and Require directives
  • Impact: Leak memory from the server process (potentially .htaccess files, session keys).
  • Apache 2.4.18 status: Exploitable – fixed in 2.4.28.

Exploit Conditions

  • Server must have Protocols h2 http/1.1 in config.
  • The attacker crafts a series of CONTINUATION frames that exceed the expected size, causing a heap overflow.

While original proofs-of-concept for this were unreliable (often leading to a DoS), refined exploits using jemalloc heap grooming can turn this into remote code execution.

Testing OptionsBleed

git clone https://github.com/hannob/optionsbleed
python3 optionsbleed.py http://victim

You will find that unless tweaked, most exploits yield limited results. This is the reality of Apache security post-2018.

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). Remote Code Execution (RCE) : An attacker can

Searching for an "apache httpd 2.4.18 exploit" today yields a confusing landscape: outdated proof-of-concepts (PoCs), references to the infamous HTTP/2 implementation flaws, and a persistent myth that this version is inherently "hackable" out-of-the-box.

This article provides a definitive, long-form analysis of the actual exploit landscape for Apache 2.4.18. We will dissect the critical CVEs, their exploitability, the limitations of public exploits, and the lessons for modern security hygiene.