What is Insertion of Sensitive Information Into (CWE-201)?

TL;DR: Insertion of Sensitive Information Into Sent Data (CWE-201) occurs when an application transmits sensitive information to another actor, leading to potential unauthorized access to confidential data.

What is Insertion of Sensitive Information Into Sent Data?

Insertion of Sensitive Information Into Sent Data (CWE-201) is a type of Broken Access Control vulnerability that occurs when an application transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor. As defined by the MITRE Corporation under CWE-201, and classified by the OWASP Foundation under A01:2025 - Broken Access Control.

Quick Summary

Insertion of Sensitive Information Into Sent Data (CWE-201) is a critical vulnerability that can lead to unauthorized access to confidential data, financial loss, or reputational damage. It occurs when an application transmits sensitive information to another actor, leading to potential unauthorized access to confidential data. To prevent CWE-201, ensure that any possibly sensitive data specified in the requirements is verified with designers to ensure that it is either a calculated risk or mitigated elsewhere.

Jump to: Quick Summary · Insertion of Sensitive Information Into Sent Data Overview · How Insertion of Sensitive Information Into Sent Data Works · Business Impact of Insertion of Sensitive Information Into Sent Data · Insertion of Sensitive Information Into Sent Data Attack Scenario · How to Detect Insertion of Sensitive Information Into Sent Data · How to Fix Insertion of Sensitive Information Into Sent Data · Framework-Specific Fixes for Insertion of Sensitive Information Into Sent Data · How to Ask AI to Check Your Code for Insertion of Sensitive Information Into Sent Data · Insertion of Sensitive Information Into Sent Data Best Practices Checklist · Insertion of Sensitive Information Into Sent Data FAQ · Vulnerabilities Related to Insertion of Sensitive Information Into Sent Data · References · Scan Your Own Site

Insertion of Sensitive Information Into Sent Data Overview

What: CWE-201 occurs when an application transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.

Why it matters: CWE-201 is a critical vulnerability that can lead to unauthorized access to confidential data, financial loss, or reputational damage.

Where it occurs: CWE-201 can occur in any application that transmits data to another actor, including web applications, APIs, mobile apps, and cloud services.

Who is affected: Any user who interacts with the vulnerable application may be affected by CWE-201.

Who is NOT affected: Applications that never construct paths/queries/commands from external input are not affected by CWE-201.

How Insertion of Sensitive Information Into Sent Data Works

Root Cause

CWE-201 occurs when an application transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.

Attack Flow

1. An attacker sends a request to the vulnerable application.
2. The application transmits sensitive information to another actor without proper validation or encryption.
3. The sensitive information is accessed by an unauthorized actor.

Prerequisites to Exploit

• The application must transmit data to another actor.
• The sensitive information must be included in the transmitted data.
• The attacker must have access to the vulnerable application and the ability to send requests.

Vulnerable Code

import requests

def transmit_data(data):
    response = requests.post('https://example.com/api/endpoint', json=data)
    return response.json()

This code transmits sensitive information to another actor without proper validation or encryption.

Secure Code

import requests
from cryptography.fernet import Fernet

def transmit_data(data, secret_key):
    encrypted_data = Fernet(secret_key).encrypt(data)
    response = requests.post('https://example.com/api/endpoint', json=encrypted_data)
    return response.json()

This code encrypts the sensitive information before transmitting it to another actor.

Business Impact of Insertion of Sensitive Information Into Sent Data

Confidentiality: CWE-201 can lead to unauthorized access to confidential data, including sensitive information such as financial data, personal identifiable information (PII), or intellectual property.

Integrity: CWE-201 can lead to modification of sensitive information, which can result in financial loss or reputational damage.

Availability: CWE-201 can lead to disruption of services, resulting in downtime and financial loss.

Insertion of Sensitive Information Into Sent Data Attack Scenario

1. An attacker sends a request to the vulnerable application.
2. The application transmits sensitive information to another actor without proper validation or encryption.
3. The sensitive information is accessed by an unauthorized actor.

How to Detect Insertion of Sensitive Information Into Sent Data

Manual Testing

• Review the application’s code and configuration for potential vulnerabilities.
• Test the application with malicious input to identify potential weaknesses.

Automated Scanners (SAST / DAST)

• Use automated scanning tools to identify potential vulnerabilities in the application’s code and configuration.

PenScan Detection

PenScan’s scanner engines actively test for CWE-201 vulnerabilities, helping you identify and fix sensitive information exposure before it’s exploited.

False Positive Guidance

To avoid false positives, ensure that any identified vulnerabilities are thoroughly reviewed and validated by a security expert.

How to Fix Insertion of Sensitive Information Into Sent Data

• Implement encryption mechanisms to protect sensitive information.
• Validate user input to prevent unauthorized access to sensitive information.
• Use allowlists to restrict access to sensitive information.

Framework-Specific Fixes for Insertion of Sensitive Information Into Sent Data

Java

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

public class TransmitData {
    public static void main(String[] args) throws Exception {
        String secretKey = "your_secret_key_here";
        Cipher cipher = Cipher.getInstance("AES");
        SecretKeySpec keySpec = new SecretKeySpec(secretKey.getBytes(), "AES");
        cipher.init(Cipher.ENCRYPT_MODE, keySpec);
        byte[] encryptedData = cipher.doFinal("sensitive_data".getBytes());
        System.out.println(encryptedData);
    }
}

Node.js

const crypto = require('crypto');
const secretKey = 'your_secret_key_here';

function transmitData(data) {
    const cipher = crypto.createCipher('aes-256-cbc', secretKey);
    let encryptedData = cipher.update(data, 'utf8', 'hex');
    encryptedData += cipher.final('hex');
    return encryptedData;
}

Python/Django

import base64
from cryptography.fernet import Fernet

def transmit_data(data):
    secret_key = "your_secret_key_here"
    fernet = Fernet(secret_key)
    encrypted_data = fernet.encrypt(data.encode())
    return encrypted_data.decode()

PHP

<?php
$secretKey = 'your_secret_key_here';
$data = 'sensitive_data';

$cipher = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC), MCRYPT_RAND);
$encryptedData = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $secretKey, $data, MCRYPT_MODE_CBC, $cipher);

echo $encryptedData;
?>

How to Ask AI to Check Your Code for Insertion of Sensitive Information Into Sent Data

You can use an AI-powered coding assistant to review your code for potential CWE-201 vulnerabilities and provide recommendations for remediation. Simply copy-paste the following prompt into the AI tool:

Review the following Python/Django code block for potential CWE-201 Insertion of Sensitive Information Into Sent Data vulnerabilities and rewrite it using encryption:

import base64
from cryptography.fernet import Fernet

def transmit_data(data):
    secret_key = "your_secret_key_here"
    fernet = Fernet(secret_key)
    encrypted_data = fernet.encrypt(data.encode())
    return encrypted_data.decode()

Insertion of Sensitive Information Into Sent Data Best Practices Checklist

✅ Verify that sensitive information is properly validated and sanitized before transmission. ✅ Use encryption mechanisms to protect sensitive information in transit. ✅ Implement allowlists to restrict access to sensitive information.

Insertion of Sensitive Information Into Sent Data FAQ

How do I prevent Insertion of Sensitive Information Into Sent Data?

To prevent Insertion of Sensitive Information Into Sent Data, ensure that any possibly sensitive data specified in the requirements is verified with designers to ensure that it is either a calculated risk or mitigated elsewhere. Any information that is not necessary to the functionality should be removed in order to lower both the overhead and the possibility of security-sensitive data being sent.

What are the consequences of Insertion of Sensitive Information Into Sent Data?

The consequences of Insertion of Sensitive Information Into Sent Data include exposure of sensitive information, which may lead to unauthorized access to confidential data, financial loss, or reputational damage.

How do I detect Insertion of Sensitive Information Into Sent Data?

To detect Insertion of Sensitive Information Into Sent Data, use a combination of manual testing and automated scanning tools that can identify sensitive information being transmitted or stored in an insecure manner.

What are the best practices for preventing Insertion of Sensitive Information Into Sent Data?

The best practices for preventing Insertion of Sensitive Information Into Sent Data include verifying return values, testing code thoroughly, and using allowlists to restrict access to sensitive information.

Can AI help me detect and prevent Insertion of Sensitive Information Into Sent Data?

Yes, AI-powered coding assistants can help you review your code for potential CWE-201 vulnerabilities and provide recommendations for remediation.

What are the related weaknesses to Insertion of Sensitive Information Into Sent Data?

The related weaknesses to Insertion of Sensitive Information Into Sent Data include Exposure of Sensitive Information to an Unauthorized Actor (CWE-200), Generation of Error Message Containing Sensitive Information (CWE-209), and Exposure of Sensitive Information Through Data Queries (CWE-202).

How do I fix Insertion of Sensitive Information Into Sent Data?

To fix Insertion of Sensitive Information Into Sent Data, implement the recommended mitigations from the Potential_Mitigations data provided.

Vulnerabilities Related to Insertion of Sensitive Information Into Sent Data

References

• MITRE CWE-201
• OWASP A01.2025 - Broken Access Control
• CAPEC-12, CAPEC-217, CAPEC-612, CAPEC-613, CAPEC-618, CAPEC-619, CAPEC-621, CAPEC-622, CAPEC-623
• NVD CVE Database

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 CWE-201 and other risks before an attacker does.