What is Failure to Sanitize Paired Delimiters (CWE-157)?

TL;DR: Failure to Sanitize Paired Delimiters (CWE-157) is a vulnerability that occurs when products do not properly handle grouping characters, leading to unexpected state issues. To fix it, implement strict input validation and output encoding.

What is Failure to Sanitize Paired Delimiters?

Failure to Sanitize Paired Delimiters (CWE-157) is a type of vulnerability where the product does not properly handle characters used to mark the beginning and ending of a group of entities, such as parentheses, brackets, and braces. As defined by the MITRE Corporation under CWE-157, this issue can lead to unexpected state issues within applications.

Quick Summary

Failure to Sanitize Paired Delimiters is a critical security flaw that occurs when grouping characters are not properly sanitized in user inputs. This vulnerability can result in data integrity issues and unexpected application behavior. Jump to: Overview · How It Works · Business Impact · Attack Scenario · Detection · Fixes

Jump to: Quick Summary · Failure to Sanitize Paired Delimiters Overview · How Failure to Sanitize Paired Delimiters Works · Business Impact of Failure to Sanitize Paired Delimiters · Failure to Sanitize Paired Delimiters Attack Scenario · How to Detect Failure to Sanitize Paired Delimiters · How to Fix Failure to Sanitize Paired Delimiters · Framework-Specific Fixes for Failure to Sanitize Paired Delimiters · How to Ask AI to Check Your Code for Failure to Sanitize Paired Delimiters · Failure to Sanitize Paired Delimiters Best Practices Checklist · Failure to Sanitize Paired Delimiters FAQ · Vulnerabilities Related to Failure to Sanitize Paired Delimiters · References · Scan Your Own Site

Failure to Sanitize Paired Delimiters Overview

What

Failure to Sanitize Paired Delimiters is a vulnerability where products do not properly handle grouping characters like parentheses, brackets, and braces.

Why it matters

This vulnerability can lead to unexpected state issues, data integrity problems, and security vulnerabilities.

Where it occurs

It commonly occurs in applications that process user inputs containing grouping elements without proper sanitization.

Who is affected

Developers and users of any application that processes untrusted input vectors with grouping characters are at risk.

Who is NOT affected

Applications that do not construct queries or commands from external input, or those using strict validation mechanisms, are less likely to be affected.

How Failure to Sanitize Paired Delimiters Works

Root Cause

The root cause lies in the failure of applications to properly sanitize grouping characters used in user inputs, leading to unexpected behavior and potential security vulnerabilities.

Attack Flow

1. Attacker injects untrusted input containing paired delimiters.
2. Application processes the input without proper sanitization.
3. Unexpected state or data integrity issues arise due to improper handling.

Prerequisites to Exploit

• The attacker must be able to inject or manipulate grouping elements in user inputs.
• The application must process these inputs without proper validation and sanitization.

Vulnerable Code

def process_input(input_str):
    # Vulnerable code: input is not sanitized before processing
    result = eval(f"({input_str})")

This code is vulnerable because it directly evaluates the user-provided string, which can contain paired delimiters leading to unexpected behavior.

Secure Code

def process_input(input_str):
    # Secure code: input is validated and sanitized before processing
    if not re.match(r'^\s*\([^\(\)]+\)\s*$', input_str):
        raise ValueError("Invalid input")
    result = eval(f"({input_str})")

This secure version ensures that the input string contains only valid paired delimiters, preventing unexpected behavior.

Business Impact of Failure to Sanitize Paired Delimiters

Integrity

Data integrity issues can arise due to improper handling of grouping characters, leading to unintended modifications or corruptions in data structures.

Availability

Unexpected application behavior caused by improperly sanitized inputs may disrupt the availability and stability of the system.

Financial, Compliance, Reputation

Financial losses, compliance penalties, and damage to reputation can result from security vulnerabilities and data integrity issues stemming from this weakness.

Failure to Sanitize Paired Delimiters Attack Scenario

1. Attacker injects a malicious input containing paired delimiters.
2. Application processes the input without proper sanitization.
3. Unexpected state or data corruption occurs due to improper handling of grouping characters.
4. The attacker exploits these issues for further attacks or disruptions.

How to Detect Failure to Sanitize Paired Delimiters

Manual Testing

• Review inputs and outputs for proper handling of grouping characters.
• Verify that input validation mechanisms are in place to sanitize paired delimiters.
• Check if output encoding is used properly to prevent injection attacks.

Automated Scanners (SAST / DAST)

Static analysis can identify potential CWE-157 vulnerabilities by looking for code patterns where untrusted inputs are processed without proper sanitization. Dynamic testing helps validate these findings in a runtime environment.

PenScan Detection

PenScan’s scanner engines such as ZAP, Nuclei, Wapiti, and Nikto can detect this vulnerability by analyzing input handling mechanisms and evaluating the application’s response to malicious inputs.

False Positive Guidance

False positives may arise if the pattern looks risky but is actually safe due to context a scanner cannot infer. Ensure that the input validation logic properly handles all possible scenarios.

How to Fix Failure to Sanitize Paired Delimiters

• Developers should anticipate that grouping elements will be injected/removed/manipulated in the input vectors of their product.
• Use an appropriate combination of denylists and allowlists to ensure only valid, expected, and appropriate input is processed by the system.
• Assume all input is malicious. Use “accept known good” input validation strategies.

Framework-Specific Fixes for Failure to Sanitize Paired Delimiters

Python

def process_input(input_str):
    if not re.match(r'^\s*\([^\(\)]+\)\s*$', input_str):
        raise ValueError("Invalid input")
    result = eval(f"({input_str})")

This secure code ensures that the input string contains only valid paired delimiters, preventing unexpected behavior.

How to Ask AI to Check Your Code for Failure to Sanitize Paired Delimiters

Failure to Sanitize Paired Delimiters Best Practices Checklist

✅ Developers should anticipate that grouping elements will be injected/removed/manipulated in the input vectors of their product.

✅ Use an appropriate combination of denylists and allowlists to ensure only valid, expected, and appropriate input is processed by the system.

✅ Assume all input is malicious. Use “accept known good” input validation strategies.

Failure to Sanitize Paired Delimiters FAQ

How does failure to sanitize paired delimiters occur?

It occurs when a product fails to properly handle characters used for grouping, such as parentheses or brackets, leading to unexpected state issues.

Why is input validation important in preventing CWE-157?

Input validation ensures only valid and expected inputs are processed by the system, reducing the risk of injection attacks.

What are the business impacts of failure to sanitize paired delimiters?

It can lead to data integrity issues, unexpected application behavior, and potential security vulnerabilities.

How does output encoding help mitigate CWE-157?

Properly quoting arguments and escaping special characters prevents malicious inputs from being executed as code.

What are the prerequisites for exploiting failure to sanitize paired delimiters?

The attacker must be able to inject or manipulate grouping elements in user input vectors.

How can I detect CWE-157 using manual testing techniques?

Manually review inputs and outputs, focusing on how grouping characters are handled and validated.

What is the primary fix for failure to sanitize paired delimiters?

Implement strict input validation and output encoding strategies to ensure proper handling of grouping elements.

Vulnerabilities Related to Failure to Sanitize Paired Delimiters

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 Failure to Sanitize Paired Delimiters and other risks before an attacker does.