How File Inclusion Attacks Still Exploit Modern Apps

A Persistent Threat in the Web Security Landscape

In the world of cybersecurity, some attack methods fade away as technology evolves, while others adapt and find new ways to survive. File inclusion attacks fall firmly into the latter category. Although security practices have advanced significantly, these attacks continue to impact modern web applications across various industries. At their core, file inclusion vulnerabilities occur when an application dynamically loads a file based on user input without proper validation or sanitization. An attacker can manipulate this input to load unintended files, leading to serious consequences like unauthorized data access or remote code execution.

There are two primary types of file inclusion attacks: Local File Inclusion (LFI) and Remote File Inclusion (RFI). LFI exploits involve accessing files already stored on the server hosting the application, while RFI attacks allow the attacker to pull and execute files hosted on an external server. Both are dangerous, but RFI tends to be more severe since it enables the introduction of entirely new malicious code into the system.

Why Legacy Code Keeps the Door Open

One of the biggest reasons file inclusion attacks are still a threat is the persistence of legacy code. Many organizations continue to rely on code written years—sometimes decades—ago. These older systems were often developed before security-by-design became a widespread practice, meaning that features like strict input validation or path restrictions may be absent.

When businesses modernize their applications, they often focus on adding new features or upgrading visible components, leaving large portions of the backend untouched. This creates a “mixed-generation” environment—modern frameworks layered over older, insecure logic. Attackers target these forgotten code paths, knowing that they may contain vulnerabilities that newer parts of the application no longer have. Even a single outdated function that allows unchecked file inclusion can undermine an otherwise robust security setup.

The Complexity of Modern Tech Stacks Creates Blind Spots

Modern applications are rarely built from scratch. Instead, they are assembled from a combination of custom code, open-source libraries, and third-party components. While this approach accelerates development, it also introduces significant risk. Every third-party component is a potential weak link—especially if it contains insecure file-handling functions.

In large, distributed development teams, it’s not uncommon for certain parts of the application to escape rigorous security reviews. Input sanitization checks may be inconsistent across modules, and dependencies may be added without thorough vetting. An attacker only needs one vulnerable component to exploit an application. In some cases, vulnerabilities arise not from the organization’s own coding practices but from an overlooked flaw in a widely used library.

Cloud and Container Environments Expand the Attack Surface

The shift to cloud infrastructure and containerized applications has changed the way web applications are deployed—but it has also introduced new risks. In Local File Inclusion attacks, an attacker might use the vulnerability to read sensitive configuration files stored in a container or on a cloud instance. These files may hold API keys, authentication tokens, or database credentials, which can be used to escalate the attack.

Remote File Inclusion becomes even more dangerous in cloud and container contexts. If a misconfigured application allows remote file execution, an attacker can introduce malicious scripts from their own server and run them within the target’s environment. This may result in a complete system takeover, enabling attackers to move laterally to linked services, alter application functionality, or acquire full administrative access to the hosting environment.

Why File Inclusion Attacks Still Work in 2025

It might seem surprising that a vulnerability first discussed decades ago is still relevant in today’s security landscape, but there are a few clear reasons. First, the underlying cause—improper input handling—is a basic coding flaw that can still slip through if developers are under time pressure or if code reviews focus more on functionality than security. Second, as tech stacks grow more complex, it becomes easier for a small misconfiguration or overlooked legacy function to open the door to exploitation.

Additionally, attackers have become more sophisticated in chaining vulnerabilities. For example, an LFI exploit might first be used to read log files, which then reveal system details or admin credentials. Those credentials could then be used to upload malicious code, effectively turning a local exploit into a remote execution scenario.

Preventing File Inclusion Attacks in Modern Environments

Preventing file inclusion attacks requires a layered and proactive defense strategy. At the development level, input validation is critical—applications should never trust user-supplied file paths. Whitelisting is a strong safeguard, allowing only approved file names or directories to be loaded. Functions that allow remote file execution should be disabled unless absolutely necessary.

Security audits should specifically target older code, ensuring that legacy functions meet modern security standards. Regular penetration testing can help identify vulnerabilities before they are exploited, and web application firewalls (WAFs) can block known attack patterns in real-time. In cloud and containerized environments, sensitive credentials should never be stored in easily accessible files, and environment variables should be properly protected.