CWE-117: Improper Output Neutralization for Logs

What is Improper Output Neutralization for Logs?

• Overview: Improper Output Neutralization for Logs (CWE-117) occurs when a software application logs data from external inputs without adequately neutralizing special elements, potentially leading to log injection attacks.

• Exploitation Methods:

• Attackers can insert malicious data into logs by crafting inputs containing special characters or escape sequences.
• Common attack patterns include injecting misleading log entries, altering log file formats, and obscuring true log information to mislead or hide malicious activities.

• Security Impact:

• Direct consequences include corrupted log files and misleading information in logs.
• Potential cascading effects involve difficulties in tracking system activities, hampering forensic analysis, and aiding attackers in covering their tracks.
• Business impact includes loss of data integrity, compromised audit trails, and potential regulatory compliance issues.

• Prevention Guidelines:

• Specific code-level fixes involve validating and sanitizing all log inputs, ensuring that special characters are properly escaped or encoded.
• Security best practices include using established logging frameworks that automatically handle input neutralization and regularly reviewing log handling code.
• Recommended tools and frameworks include using libraries that provide safe logging functions, such as Log4j for Java or Winston for Node.js, which have built-in mechanisms to handle input neutralization securely.

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Technical Details

Likelihood of Exploit: Medium

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Applications typically use log files to store a history of events or transactions for later review, statistics gathering, or debugging. Depending on the nature of the application, the task of reviewing log files may be performed manually on an as-needed basis or automated with a tool that automatically culls logs for important events or trending information.

Vulnerable Code Example

JavaScript Example

const fs = require('fs');

function logUserAction(userInput) {
    // Vulnerable code: directly logs user input without sanitization or escaping
    const logMessage = `User action: \${userInput}`;
    fs.appendFile('app.log', logMessage + '\n', (err) => {
        if (err) throw err;
    });
}

// Example usage
logUserAction("Login attempt\nError: Invalid credentials\n");

Explanation of Vulnerability:

• Issue: The application logs user input directly without any sanitization or escaping, which can lead to log injection attacks.
• Impact: An attacker could manipulate log files by injecting special characters or new lines, potentially obscuring log data or misleading log analysis tools.

How to fix Improper Output Neutralization for Logs?

To fix this vulnerability, you should:

1. Sanitize Input: Ensure that any user input is properly sanitized before logging.
2. Escape Special Characters: Use a logging library that automatically escapes special characters or implement escaping of characters like new lines (\n) and carriage returns (\r).
3. Use Structured Logging: Consider using a structured logging format (e.g., JSON) to avoid issues with log injection.

Fixed Code Example

const fs = require('fs');

// Function to escape special characters in log messages
function sanitizeForLog(input) {
    // Replace newline and carriage return characters with a space
    return input.replace(/[\n\r]/g, ' ').replace(/[\x00-\x1F\x7F]/g, '');
}

function logUserAction(userInput) {
    // Fixed code: sanitize user input to prevent log injection
    const sanitizedInput = sanitizeForLog(userInput);
    const logMessage = `User action: \${sanitizedInput}`;
    fs.appendFile('app.log', logMessage + '\n', (err) => {
        if (err) throw err;
    });
}

// Example usage
logUserAction("Login attempt\nError: Invalid credentials\n");

Explanation of Fix:

• Sanitization: The sanitizeForLog function replaces newline characters (\n, \r) and other control characters with a space, preventing them from being logged directly.
• Improved Security: By sanitizing the input before logging, we mitigate the risk of log injection attacks, ensuring the integrity of log files.
• Structured Logging: Although not implemented here, using structured logging (e.g., JSON) can further enhance log security by enforcing a strict format and escaping special characters automatically.