Apache HTTP Server 2.4.18 is a widely-used web server, but it contains four significant security vulnerabilities that put thousands of websites at risk. One of these vulnerabilities is rated CRITICAL, meaning attackers could potentially gain unauthorized access to sensitive data or crash your website entirely. If your website is running Apache 2.4.18, you need to take action immediately to protect your business, your users, and your reputation.
In this guide, we'll explain what these vulnerabilities are, who they affect, and most importantly, how to fix them. Whether you're a website owner, a system administrator, or a developer, understanding these security risks is crucial for keeping your digital infrastructure safe. We'll walk you through everything step-by-step so you can secure your server with confidence.
Apache HTTP Server is the most popular web server software in the world, used by millions of websites to serve web pages and applications to visitors. Think of it as the engine that powers your website—it's the software running on your server that processes requests from visitors' browsers and delivers your web pages to them. Apache 2.4.18 is a specific version released to improve performance and add new features, including support for HTTP/2, a faster protocol for loading websites.
However, Apache 2.4.18 was released before several critical security flaws were discovered in the HTTP/2 module (mod_http2). These vulnerabilities allow attackers to exploit weaknesses in how the server handles certain types of requests. The problems range from memory leaks that could crash your server, to bypassing security checks that protect sensitive data, to exhausting server resources. Because over 5,700 websites still run this version, it's a popular target for cybercriminals looking for easy entry points.
4 CVEs found. The most critical are explained below.
Apache 2.4.18-2.4.39 has a flaw where the server can read memory that has already been freed when closing HTTP/2 connections. This happens only with specially crafted network input. An attacker could exploit this vulnerability to crash your server or potentially steal sensitive information from server memory.
Impact: Your website could go down unexpectedly, or attackers could access confidential data like passwords or API keys stored in server memory.
↗ View on NVDWhen both mod_http2 and SSL security are enabled, the server doesn't properly verify client certificates for HTTP/2 requests. This means someone could access restricted areas of your website that should require authentication. The vulnerability affects versions 2.4.18 through 2.4.20.
Impact: Unauthorized users could access private or restricted content on your website that should be protected by client certificate requirements.
↗ View on NVDBy sending specially crafted HTTP/2 requests, attackers can trick your server into holding onto worker processes for 60 seconds longer than necessary. Once enough workers are used up this way, your website becomes unable to handle legitimate visitor requests. This affects versions 2.4.18-2.4.30 and 2.4.33.
Impact: Your website could become slow or completely unavailable to real customers as the server runs out of capacity to handle requests.
↗ View on NVDApache 2.4.17-2.4.18 with mod_http2 enabled doesn't limit how many simultaneous request streams one HTTP/2 connection can create. An attacker can open one connection and create thousands of streams to exhaust server resources. This causes your server to stop processing legitimate requests.
Impact: Your website becomes unavailable to real users as attackers consume all available server processing capacity with a single connection.
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Apache 2.4.18 poses a serious security risk to your website and your visitors. The four vulnerabilities we've discussed can lead to data theft, service interruptions, and reputational damage. Fortunately, the fix is straightforward: update to Apache 2.4.34 or later. This should be a priority task on your security to-do list.
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