Classified as a "Use-After-Free" vulnerability, Optionsbleed affects Apache HTTP Server through 2.2.34 and 2.4.x through 2.4.27. The bug occurs when an unrecognized HTTP method is placed in a <Limit method> directive within an .htaccess file, corrupting the global methods table and leading to in the Allow header response.
| CVE ID | Description | Impact | Exploit Status | | :--- | :--- | :--- | :--- | | CVE-2016-5387 | HTTP_PROXY environment variable injection via "Proxy" header ("httpoxy"). | High – Remote redirection of outbound HTTP traffic to a malicious proxy. | Public exploit code & testing tools. | | CVE-2017-9798 | Use-after-free when using an <Limit> directive with an unrecognized HTTP method in .htaccess ("Optionsbleed"). | High – Remote reading of server memory, potentially exposing sensitive data. | Metasploit module & public PoC. | | CVE-2016-4979 | X.509 client certificate authentication bypass when using HTTP/2. | High – Unauthorized access to protected resources. | Proof-of-concept code available. | | CVE-2016-8743 | Overly permissive whitespace parsing in HTTP requests. | High – Request smuggling, response splitting, and cache pollution attacks. | No public exploit, but attack vectors are well-understood. | | CVE-2016-1546 | Unbounded number of simultaneous stream workers for a single HTTP/2 connection, when mod_http2 is enabled. | Medium – Denial of service (stream-processing outage). | No public exploit; potential for DoS attacks. | | CVE-2016-8740 | Unbounded memory consumption via crafted CONTINUATION frames in HTTP/2 requests. | Medium – Denial of service (memory exhaustion). | No public exploit; potential for DoS attacks. | | CVE-2017-15715 | <FilesMatch> directive bypass using a trailing newline character in the filename. | Low – Bypassing file access restrictions. | No public exploit; local file access risks. |
Released in late 2015, Apache HTTP Server 2.4.18 was a popular version of the industry-standard web server. However, as with all software, vulnerabilities were discovered in the months and years following its release. Exploits targeting Apache HTTPD 2.4.18 often center around , improper HTTP/2 handling , and security configuration bypasses .
Let’s ground this in reality. In 2020, a bug bounty hunter reported an "Apache 2.4.18 exploit" against a Fortune 500 company. The server returned Server: Apache/2.4.18 (Ubuntu) . apache httpd 2.4.18 exploit
While remote code execution (RCE) is rare in stock 2.4.18, local privilege escalation (LPE) is a real vector if an attacker already has low-privileged shell access (e.g., via an exploited PHP/WordPress site).
Deep Dive: Understanding the Apache HTTPD 2.4.18 Exploit Ecosystem
When compiled and run as www-data on a 2.4.18 server, this exploit has historically yielded root shells on unpatched Ubuntu 16.04 installations. | High – Remote redirection of outbound HTTP
To scan a network perimeter and automatically flag this vulnerable service, administrators use the Nmap Network Mapper: nmap -sV --script http-server-header -p 80,443 target-ip Use code with caution.
To mitigate the risks associated with the Apache HTTPD 2.4.18 exploit, several steps can be taken:
The attacker alters the scoreboard array, specifically targeting the worker process structures to force an out-of-bounds array access. | High – Remote reading of server memory,
curl -I http://target-domain.com # Look for: Server: Apache/2.4.18 (Ubuntu) Use code with caution.
To elevate privileges, an attacker must first obtain low-level execution context on the server (e.g., through a separate web application vulnerability, like an arbitrary PHP file upload or a Local File Inclusion exploit).
A distinct DoS vulnerability reported by security researchers indicates that versions 2.4.17 and 2.4.18 can experience extended thread-blocking under certain connection conditions.
that exposes systems to critical risks, including local root privilege escalation, authentication bypass, and severe Denial of Service (DoS) attacks . Released in late 2015, this specific build of the Apache HTTP Server contains fundamental design flaws within its core engine and popular modules like mod_http2 and mod_status . Because version 2.4.18 remains embedded in old enterprise environments and unpatched Linux distributions, understanding its exploit vectors is vital for security teams performing penetration testing or modernizing legacy infrastructure. Major Vulnerabilities and Exploit Mechanisms