Local File Inclusion (LFI) is a type of vulnerability in web applications that occurs when an attacker manipulates the application into including files from the server’s filesystem.
What Causes a Local File Inclusion (LFI) Vulnerability?
An LFI vulnerability typically arises when a plugin or application fails to properly sanitize and validate user input. This allows attackers to exploit the flaw by passing specially crafted filenames, enabling them to traverse directories or include sensitive files. Misconfigured server settings can also exacerbate the risk of LFI exploitation.
LFI can be especially dangerous if users have the ability to upload files, regardless of file extensions. For example, if a file like image.png contains PHP code and is included using PHP functions such as include or require, any PHP code within that file can still be executed.
What Can Happen If Your WordPress Website Has an LFI Vulnerability?
The impact of an LFI vulnerability on your WordPress site largely depends on the files present and whether users are able to upload their own files. Generally, the severity of this vulnerability ranges from medium to high.
Hackers commonly exploit LFI vulnerabilities to access configuration files like wp-config.php or the /etc/passwd file, both of which contain critical information, such as server credentials and other sensitive data.
If the website has a file upload feature, attackers can use LFI to inject backdoors and ultimately take over the entire website. LFI vulnerabilities are frequently targeted by attackers. A recent example is a vulnerability found in the ReHub Theme, which allowed unauthenticated LFI exploitation: ReHub Theme vulnerability.
How Can WordPress Developers Prevent LFI Vulnerabilities?
For plugin developers, preventing LFI vulnerabilities boils down to proper input validation. You can ensure that input contains only letters using ctype_alpha(), or remove potentially harmful characters like slashes and dots. However, the exact solution depends on how the file inclusion function is implemented.
For website administrators, it is crucial to:
- Regularly monitor plugins for vulnerabilities and apply patches as soon as they are released.
- Use a high-quality managed WordPress hosting service, where proper server configurations help mitigate the risk of LFI exploitation.
Conclusion
Local File Inclusion (LFI) is a serious vulnerability that can allow attackers to access sensitive files, inject malicious code, and even take over the site. Proper input validation and sanitization are critical for developers to prevent such vulnerabilities, while website administrators should stay vigilant by regularly updating plugins and use high-quality WordPress hosting services.
Oliver Sild
Oliver Sild is the CEO and Co-founder of Patchstack. He is an entrepreneur and cyber security expert with a strong focus on community building. He has been organising hacking competitions (& local CTF community) in Estonia since 2016, has kickstarted a startup community in his hometown and has nearly 10 years of experience with WordPress security.
