What is Partial String Comparison (CWE-187)?

TL;DR: Partial String Comparison (CWE-187) is a security flaw where only part of a string is compared, leading to resultant weaknesses. To mitigate this vulnerability, ensure full comparison of strings.

What is Partial String Comparison?

Partial String Comparison (CWE-187) is a type of security flaw where the product performs a comparison that only examines a portion of a factor before determining whether there is a match, such as a substring. This can lead to resultant weaknesses by allowing attackers to bypass validation checks and manipulate input strings.

As defined by the MITRE Corporation under CWE-187, and classified by the OWASP Foundation under no official mapping…

Quick Summary

Partial String Comparison (CWE-187) is a security flaw where only part of a string is compared. This can lead to resultant weaknesses by allowing attackers to bypass validation checks and manipulate input strings. It impacts system integrity and access control mechanisms, compromising data modifications.

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

Partial String Comparison Overview

What

Partial String Comparison (CWE-187) occurs when a comparison only examines part of a string, leading to resultant weaknesses.

Why it matters

This vulnerability can allow attackers to bypass validation checks by manipulating input strings, compromising system integrity and access control mechanisms.

Where it occurs

It commonly occurs in applications that perform partial comparisons for validation purposes.

Who is affected

Applications that use partial string comparisons are at risk of security vulnerabilities.

Who is NOT affected

Systems already using robust comparison methods or those not performing partial string comparisons are unaffected.

How Partial String Comparison Works

Root Cause

The root cause lies in comparing only a portion of a string rather than its entirety, which allows for potential security weaknesses.

Attack Flow

1. Attacker identifies a partial string comparison.
2. Manipulates input to bypass validation checks.
3. Gains unauthorized access or modifies data.

Prerequisites to Exploit

• The application must perform partial string comparisons.
• Input can be manipulated by the attacker.

Vulnerable Code

def validate_input(input):
    if input.startswith('valid'):
        return True

This code only checks if the input starts with “valid”, allowing attackers to bypass validation by manipulating the rest of the string.

Secure Code

def validate_input(input):
    if input == 'valid':
        return True

The secure version ensures full comparison of strings, preventing attackers from bypassing validation checks.

Business Impact of Partial String Comparison

Integrity

Partial string comparisons can lead to unauthorized data modifications by bypassing validation checks.

Access Control

Compromises system integrity and access control mechanisms, allowing unauthorized access or data manipulation.

Availability

Impact on availability is minimal unless the vulnerability leads to a denial-of-service condition.

• Financial loss due to compromised data.
• Compliance penalties for security breaches.
• Reputation damage from publicized vulnerabilities.

Partial String Comparison Attack Scenario

1. Attacker identifies partial string comparison in application code.
2. Manipulates input to bypass validation checks.
3. Gains unauthorized access or modifies data, compromising system integrity and access control mechanisms.

How to Detect Partial String Comparison

Manual Testing

• Check for functions that only partially compare strings without validating the entire input.
• Review code for partial string comparisons in conditional statements.

Automated Scanners (SAST / DAST)

Static analysis can detect partial string comparisons, while dynamic testing verifies actual behavior during runtime.

PenScan Detection

PenScan’s scanner engines such as ZAP and Wapiti actively test for this issue.

False Positive Guidance

A real finding will show a comparison of only part of the input string without proper validation. A false positive may occur if partial comparisons are used in non-security contexts.

How to Fix Partial String Comparison

• Ensure full comparison of strings before making decisions based on them.
• Implement robust validation checks that cover entire inputs, not just parts.

Framework-Specific Fixes for Partial String Comparison

Python/Django

def validate_input(input):
    if input == 'valid':
        return True

This ensures the entire string is compared rather than a partial substring.

How to Ask AI to Check Your Code for Partial String Comparison

Partial String Comparison Best Practices Checklist

• Ensure full comparison of strings before making decisions based on them.
• Implement robust validation checks that cover entire inputs, not just parts.

Partial String Comparison FAQ

How does partial string comparison lead to security vulnerabilities?

Partial string comparison can be exploited by attackers who manipulate input strings to bypass validation checks, leading to unauthorized access or data manipulation.

What is the root cause of CWE-187?

The root cause lies in comparing only a portion of a string rather than its entirety, which allows for potential security weaknesses.

Can you provide an example of vulnerable code for partial string comparison?

Vulnerable code might compare just part of a user input to validate it, allowing attackers to bypass checks by manipulating the rest of the string.

How can I detect partial string comparisons in my application?

You can use static analysis tools or manual reviews to check for functions that only partially compare strings without validating the entire input.

What are some best practices to prevent CWE-187?

Always validate and sanitize user inputs thoroughly, ensuring full comparison of strings before making decisions based on them.

How does partial string comparison impact system integrity?

Partial string comparisons can lead to unauthorized data modifications by bypassing validation checks, compromising the integrity of your application’s data.

What is a common mistake when fixing CWE-187?

A common mistake is implementing a simple substring check instead of validating the entire input string, which does not effectively mitigate the vulnerability.

Vulnerabilities Related to Partial String Comparison

| CWE | Name | Relationship | |—|—|—| | CWE-1023 | Incomplete Comparison with Missing Factors (ChildOf) |

References

• MITRE
• CAPEC
• 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 Partial String Comparison and other risks before an attacker does.