File Inclusion Vulnerability via "Include $file"

[KanjiHall]

Report on Path Traversal Vulnerability in PHP Code

Vulnerability Overview: The provided PHP code is vulnerable to a path traversal attack through the include function. This vulnerability arises due to the lack of proper input validation on the variable $file before passing it to the include statement, allowing an attacker to traverse the file system and potentially execute arbitrary PHP code.

Code Analysis: Below is the vulnerable code snippet from the provided URL:

$file = $page . '.php';
// ...

if (!file_exists($file)) {
    header('HTTP/1.0 404 Not Found');
    $file = '_run/404.php';
}

// ...

include $file;

In this code:

1. The variable $page is used to construct the filename $file by appending the .php extension.
2. The script checks if the file exists using file_exists.
3. If the file does not exist, it defaults to including the _run/404.php file.

Vulnerability Details: An attacker can exploit this code by manipulating the $page variable to include arbitrary files outside of the intended directory. Since there is no proper validation or sanitization of user input, an attacker could craft a request with a specially crafted $page value to traverse the file system and potentially execute unauthorized PHP code.

For example, an attacker could make a request with a malicious $page value like "../../../../../etc/passwd", leading to an attempt to include the sensitive /etc/passwd file.

Recommendations for Mitigation: To address this vulnerability, it is crucial to validate and sanitize user input before using it to construct file paths. Implementing proper input validation helps ensure that only allowed and safe filenames are included.

One effective approach is to use a whitelist of allowed filenames or directories and reject any input that falls outside these boundaries. Additionally, consider using an absolute path or a predefined base directory to prevent path traversal.

Patch Suggestion:

$allowedPages = ['index', 'about', 'contact']; // Add allowed pages to the whitelist

$page = rtrim(substr($request['path'], strlen('/nouislider/')), '/');
if (!$page || !in_array($page, $allowedPages)) {
    $page = 'index';
}

$file = $page . '.php';
// ...

This patch uses a whitelist of allowed page names to ensure that only valid and safe pages can be included. If the requested page is not in the whitelist, it defaults to the 'index.php' page.

Conclusion: It is crucial to implement proper input validation and sanitization to prevent path traversal vulnerabilities. Applying the suggested patch helps mitigate the risk of including unauthorized files through the include function. Regular security audits and code reviews are recommended to identify and address potential vulnerabilities in PHP applications.

References:

• OWASP - Testing for Local File Inclusion
• OWASP - Testing for File Inclusion

[leongersen]

The php code for the documentation merely generates static pages, and does not run in a production environment.

[github-actions[bot]]

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