CWE-147: Improper Neutralization of Input Terminators

What is Improper Neutralization of Input Terminators?

• Overview: Improper Neutralization of Input Terminators (CWE-147) occurs when a software product receives input containing special elements that act as terminators in a protocol or data format, but fails to properly handle or sanitize these elements before passing them to another component. This can lead to unexpected behavior or vulnerabilities.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting input that includes special terminator elements, causing the system to prematurely terminate or misinterpret data.
• Common attack patterns include inserting null characters or specific terminators like "." in SMTP to alter the control flow or data processing of an application.

• Security Impact:

• Direct consequences of successful exploitation can include denial of service, unauthorized access, or data corruption.
• Potential cascading effects might involve broader system disruption or the exposure of sensitive data.
• Business impact could range from operational downtime to loss of customer trust and legal compliance issues.

• Prevention Guidelines:

• Specific code-level fixes include validating and sanitizing input to ensure that terminators are either removed or properly escaped before processing.
• Security best practices involve employing input validation libraries and frameworks that handle these terminators safely.
• Recommended tools and frameworks include those specializing in input validation and sanitation, such as OWASP ESAPI or custom validation routines tailored to your application's needs.

Corgea can automatically detect and fix Improper Neutralization of Input Terminators in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

JavaScript Example

function sendMessage(userInput) {
    // Vulnerable: This code does not neutralize input terminators like newline characters
    const message = `SEND \${userInput}\n`;
    // Sending message to downstream component
    sendToComponent(message);
}

function sendToComponent(data) {
    // Simulates sending data to a downstream component
    console.log("Data sent: " + data);
}

sendMessage("Hello, world!\nQUIT"); // Malicious input could disrupt the message processing

Explanation:

• The vulnerability here is that the userInput is directly embedded into the command string without neutralizing special characters such as newline \n.
• This allows an attacker to inject a newline to prematurely terminate messages, potentially disrupting the communication protocol, leading to unexpected behavior or security breaches.

How to fix Improper Neutralization of Input Terminators?

To fix this vulnerability, it's essential to sanitize and properly encode the input to neutralize special characters that can act as input terminators. This involves:

1. Stripping or encoding newline characters and other control characters that might interfere with the communication protocol.
2. Using functions that safely handle and encode user inputs, preventing them from affecting the intended message structure.

Fixed Code Example

function sendMessage(userInput) {
    // Fix: Neutralize input terminators by removing newline characters
    const sanitizedInput = userInput.replace(/[\n\r]/g, '');
    const message = `SEND \${sanitizedInput}\n`;
    // Sending message to downstream component
    sendToComponent(message);
}

function sendToComponent(data) {
    // Simulates sending data to a downstream component
    console.log("Data sent: " + data);
}

sendMessage("Hello, world!\nQUIT"); // Now malicious input is sanitized

Explanation:

• The fix involves using a regular expression to remove newline characters from userInput before it is embedded into the message ({3}).
• This ensures that any potentially malicious input terminators are neutralized, preventing them from prematurely terminating the command sequence.