Apache HTTP Server Vulnerabilities and Confusion Attacks Exposed

Posted on August 11, 2024

A recent research presentation at Black Hat USA 2024 has brought to light serious architectural vulnerabilities in the Apache HTTP Server, a cornerstone of web infrastructure worldwide. Conducted by cybersecurity researcher Orange Tsai, the study delved deep into the complexities of Apache’s modular design, uncovering a series of critical weaknesses that could expose millions of servers to cyberattacks.

The Complexity of Apache HTTP Server

Apache HTTP Server operates through a highly modular architecture, where hundreds of small modules work in tandem to handle HTTP requests. These modules share a request_rec structure for synchronization, communication, and data exchange. While this design enables efficiency and scalability, it also introduces significant complexity, especially when scaled to a large number of modules. This complexity can create security gaps, making the system vulnerable to various forms of exploitation.

Key Findings: Nine New Vulnerabilities

The research identified nine previously undisclosed vulnerabilities in the Apache HTTP Server, each posing a unique threat:

  1. CVE-2024-38472: A Server-Side Request Forgery (SSRF) vulnerability in Apache HTTP Server on Windows. This flaw allows attackers to manipulate internal server requests, potentially leading to unauthorized access to internal services.
  2. CVE-2024-39573: Proxy encoding issues that could enable attackers to bypass security mechanisms and gain unauthorized access.
  3. CVE-2024-38477: A vulnerability in the mod_proxy module where a specially crafted request can cause a crash, leading to Denial of Service (DoS).
  4. CVE-2024-38476: Exploitation of malicious backend application output via internal redirects, potentially compromising the system.
  5. CVE-2024-38475: A weakness in mod_rewrite that can be exploited when the first segment of the substitution matches the filesystem path.
  6. CVE-2024-38474: Handling issues with encoded question marks in backreferences, which could be exploited to bypass security controls.
  7. CVE-2024-38473: Another proxy encoding problem that could lead to security vulnerabilities.
  8. CVE-2023-38709: HTTP response splitting vulnerability, allowing attackers to manipulate the server’s responses.
  9. CVE-2024-??????: An as-yet unpatched vulnerability that remains a significant concern.

Confusion Attacks: A New Class of Threats

The research also introduced a new class of vulnerabilities called Confusion Attacks. These attacks exploit inconsistencies in how different modules within Apache HTTP Server interpret the same fields, leading to security risks such as access control bypasses and arbitrary code execution.

  1. Filename Confusion: This attack occurs when different modules interpret the r->filename field inconsistently—some treat it as a URL, while others see it as a filesystem path. This can lead to path truncation, ACL bypass, and the execution of unauthorized scripts.
  2. DocumentRoot Confusion: This attack exploits the confusion between paths with and without the DocumentRoot prefix, potentially leading to unintended file access and security breaches such as XSS, LFI, SSRF, or even RCE.
  3. Handler Confusion: This vulnerability arises from the interchangeable use of AddType and AddHandler directives, leading to potential overwrites or misuse of handlers, resulting in issues like SSRF, RCE, or access to local Unix domain sockets.

Mitigation and Recommendations

Given the severity of these vulnerabilities, organizations using Apache HTTP Server are strongly advised to update their servers to the latest version (2.4.60) and carefully review their configurations to mitigate these risks. The research emphasizes the importance of understanding the internal mechanisms and architectural design of critical software like Apache HTTP Server. By exposing these vulnerabilities, the research aims to help organizations fortify their defenses against potential exploitation and improve overall cybersecurity resilience.

Source: Cyber Security News

The European Cyber Intelligence Foundation is a nonprofit think tank specializing in intelligence and cybersecurity, offering consultancy services to government entities. To mitigate potential threats, it is important to implement additional cybersecurity measures with the help of a trusted partner like INFRA www.infrascan.net, or you can try yourself using check.website.