What is Exposure of File Descriptor (CWE-403)?

TL;DR: Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) (CWE-403) is a security flaw where sensitive file descriptors remain open when invoking child processes, leading to unauthorized I/O operations. Fix by closing or securely managing file descriptor inheritance.

What is Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)?

Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) (CWE-403) is a type of vulnerability that occurs when sensitive file descriptors are not closed before invoking a child process, allowing the child to perform unauthorized I/O operations. As defined by the MITRE Corporation under CWE-403.

Quick Summary

Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) allows an attacker to read or modify data through inherited file descriptors. This can lead to significant security breaches and system integrity issues. Jump to: Overview · How It Works · Business Impact · Attack Scenario · Detection · Fix · Framework-Specific Fixes · Ask AI · Best Practices Checklist · FAQ · Related Vulnerabilities

Jump to: Quick Summary · Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Overview · How Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Works · Business Impact of Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) · Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Attack Scenario · How to Detect Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) · How to Fix Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) · Framework-Specific Fixes for Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) · How to Ask AI to Check Your Code for Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) · Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Best Practices Checklist · Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) FAQ · Vulnerabilities Related to Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) · References · Scan Your Own Site

Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Overview

What: A process does not close sensitive file descriptors before invoking a child process, allowing the child to perform unauthorized I/O operations.

Why it matters: Unauthorized access can lead to data breaches and system integrity issues.

Where it occurs: Primarily in Unix-like systems and Windows environments where processes are frequently spawned.

Who is affected: Applications that spawn subprocesses without proper file descriptor management are at risk.

Who is NOT affected: Systems with strict process isolation or those using secure methods for managing file descriptors.

How Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Works

Root Cause

A process fails to close sensitive file descriptors before invoking a child process, leaving them accessible to the child.

Attack Flow

1. An attacker identifies an application that spawns subprocesses.
2. The attacker exploits the open file descriptors to perform unauthorized I/O operations on inherited resources.

Prerequisites to Exploit

• A parent process with open file descriptors.
• A child process spawned without proper closure of sensitive descriptors.

Vulnerable Code

import os
fd = os.open('/path/to/sensitive/file', os.O_RDONLY)
os.fork()  # Child inherits the open file descriptor

This code does not close the file descriptor before forking, leaving it accessible to the child process.

Secure Code

import os
fd = os.open('/path/to/sensitive/file', os.O_RDONLY)
pid = os.fork()
if pid == 0:
    # Child process
else:
    os.close(fd)  # Close file descriptor in parent process

The secure code ensures that the file descriptor is closed in the parent process before forking.

Business Impact of Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)

Confidentiality: Unauthorized access to sensitive data through inherited file descriptors can lead to data breaches.

• Example: An attacker reads confidential files via an open descriptor.

Integrity: Data corruption due to unauthorized I/O operations on inherited file descriptors.

• Example: An attacker modifies critical system configuration files using a leaked descriptor.

Business Consequences

1. Financial loss from stolen intellectual property or sensitive data.
2. Non-compliance with regulatory requirements for data protection.
3. Damage to reputation and trust among customers due to security breaches.

Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Attack Scenario

1. An attacker identifies a system that spawns subprocesses without proper file descriptor management.
2. The attacker exploits the open descriptors to read sensitive files or modify critical configuration files.
3. Unauthorized operations are performed, leading to data breaches and system integrity issues.

How to Detect Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)

Manual Testing

• Review code for instances where file descriptors are opened before process spawning.
• Ensure proper closure of sensitive file descriptors in parent processes.

Automated Scanners (SAST / DAST)

Static analysis can identify code patterns indicating potential file descriptor leaks. Dynamic testing is necessary to confirm actual exploitation scenarios.

PenScan Detection

PenScan’s scanner engines ZAP, Nuclei, Wapiti, Nikto, SSLyze, and Dalfox may detect this vulnerability during automated scans.

False Positive Guidance

A false positive occurs if a file descriptor appears open but is actually managed securely by the application’s design.

How to Fix Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)

• Ensure proper closure of sensitive file descriptors before spawning child processes.
• Use secure methods for managing file descriptor inheritance in subprocesses.

Framework-Specific Fixes for Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)

Python/Django

import os
fd = os.open('/path/to/sensitive/file', os.O_RDONLY)
pid = os.fork()
if pid == 0:
    # Child process
else:
    os.close(fd)  # Close file descriptor in parent process

Ensure that sensitive file descriptors are closed before forking to prevent leaks.

How to Ask AI to Check Your Code for Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)

Review the following Python code block for potential CWE-403 Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) vulnerabilities and rewrite it using secure file descriptor management:

Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) Best Practices Checklist

✅ Ensure sensitive file descriptors are closed before spawning child processes.

✅ Use secure methods for managing file descriptor inheritance in subprocesses.

✅ Implement strict process isolation and manage file descriptors carefully.

✅ Regularly audit code for proper handling of file descriptors during process management.

Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) FAQ

How does a file descriptor leak occur?

A file descriptor leak occurs when a process fails to close sensitive file descriptors before invoking a child process, allowing the child to perform unauthorized I/O operations using those descriptors.

Why is Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) dangerous?

It allows an attacker to read or modify sensitive data through unauthorized I/O operations on inherited file descriptors.

Can you provide an example of vulnerable code for CWE-403?

Vulnerable code fails to close file descriptors before executing a child process, leaving them accessible to the child.

What are some common scenarios where file descriptor leaks happen?

Common scenarios include improperly managed subprocesses and inter-process communication without proper closure of file handles.

How can developers prevent Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) in their applications?

Developers should ensure that sensitive file descriptors are closed before invoking child processes or using secure methods to manage file descriptor inheritance.

What is the impact of an Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) vulnerability on system integrity?

Unauthorized I/O operations can lead to data corruption, compromising system integrity and confidentiality.

How does PenScan detect Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) in web applications?

PenScan uses static analysis to identify code patterns that indicate potential file descriptor leaks.

Vulnerabilities Related to Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’)

References

• MITRE
• NVD

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Exposure of File Descriptor to Unintended Control Sphere (‘File Descriptor Leak’) and other risks before an attacker does.