CAPEC-193 PHP Remote File Inclusion

CAPEC ID: 193

CAPEC-193 Metadata

Likelihood of Attack

High

Typical Severity

High

Overview

Summary

In this pattern the adversary is able to load and execute arbitrary code remotely available from the application. This is usually accomplished through an insecurely configured PHP runtime environment and an improperly sanitized "include" or "require" call, which the user can then control to point to any web-accessible file. This allows adversaries to hijack the targeted application and force it to execute their own instructions.

Prerequisites

Target application server must allow remote files to be included in the "require", "include", etc. PHP directives The adversary must have the ability to make HTTP requests to the target web application.

Execution Flow

Step Phase Description Techniques
1 Explore [Survey application] Using a browser or an automated tool, an adversary follows all public links on a web site. They record all the links they find.
  • Use a spidering tool to follow and record all links. Make special note of any links that include parameters in the URL.
  • Use a proxy tool to record all links visited during a manual traversal of the web application. Make special note of any links that include parameters in the URL. Manual traversal of this type is frequently necessary to identify forms that are GET method forms rather than POST forms.
  • Use a browser to manually explore the website and analyze how it is constructed. Many browser's plugins are available to facilitate the analysis or automate the URL discovery.
2 Experiment [Attempt variations on input parameters] The attack variants make use of a remotely available PHP script that generates a uniquely identifiable output when executed on the target application server. Possibly using an automated tool, an adversary requests variations on the inputs they surveyed before. They send parameters that include variations of payloads which include a reference to the remote PHP script. They record all the responses from the server that include the output of the execution of remote PHP script.
  • Use a list of probe strings to inject in parameters of known URLs. The probe strings are variants of PHP remote file inclusion payloads which include a reference to the adversary controlled remote PHP script.
  • Use a proxy tool to record results of manual input of remote file inclusion probes in known URLs.
3 Exploit [Run arbitrary server-side code] As the adversary succeeds in exploiting the vulnerability, they are able to execute server-side code within the application. The malicious code has virtual access to the same resources as the targeted application. Note that the adversary might include shell code in their script and execute commands on the server under the same privileges as the PHP runtime is running with.
  • Develop malicious PHP script that is injected through vectors identified during the Experiment Phase and executed by the application server to execute a custom PHP script.

Potential Solutions / Mitigations

Implementation: Perform input validation for all remote content, including remote and user-generated content Implementation: Only allow known files to be included (allowlist) Implementation: Make use of indirect references passed in URL parameters instead of file names Configuration: Ensure that remote scripts cannot be include in the "include" or "require" PHP directives

Related Weaknesses (CWE)

CWE ID Description
CWE-80 Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
CWE-98 Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion')

Related CAPECs

CAPEC ID Description
CAPEC-253 The attacker forces an application to load arbitrary code files from a remote location. The attacker could use this to try to load old versions of library files that have known vulnerabilities, to load malicious files that the attacker placed on the remote machine, or to otherwise change the functionality of the targeted application in unexpected ways.

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