What is Buffer Over-read (CWE-126)?

TL;DR: Buffer Over-read is a type of vulnerability that occurs when an application reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer. It can be fixed by implementing secure coding techniques, such as bounds checking and input validation.

At-a-Glance

What is Buffer Over-read?

Buffer Over-read (CWE-126) is a type of vulnerability that occurs when an application reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer. As defined by the MITRE Corporation under CWE-126, and classified by the OWASP Foundation under None…

Quick Summary

Buffer Over-read is a critical security vulnerability that can lead to confidentiality breaches, integrity violations, and denial-of-service attacks. It occurs when an application reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer. To fix Buffer Over-read, you need to implement secure coding techniques, such as bounds checking and input validation.

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

Buffer Over-read Overview

What: Buffer Over-read is a type of vulnerability that occurs when an application reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.

Why it matters: Buffer Over-read can lead to confidentiality breaches, integrity violations, and denial-of-service attacks. It is a critical security vulnerability that requires immediate attention.

Where it occurs: Buffer Over-read typically occurs in applications that use buffers to store data, such as strings or arrays.

Who is affected: Any application that uses buffers to store data is potentially vulnerable to Buffer Over-read.

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

How Buffer Over-read Works

Root Cause

Buffer Over-read occurs when an application reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.

Attack Flow

1. The attacker sends a malicious request to the application.
2. The application reads from a buffer using buffer access mechanisms such as indexes or pointers.
3. The buffer is accessed beyond its bounds, allowing the attacker to read sensitive data.

Prerequisites to Exploit

• The attacker must be able to send a malicious request to the application.
• The application must use buffers to store data.
• The buffer must not have proper bounds checking and input validation.

Vulnerable Code

char *buf = malloc(10);
strcpy(buf, "Hello, World!");
printf("%s", buf + 5); // Accessing memory location after the targeted buffer

This code is vulnerable to Buffer Over-read because it accesses a buffer beyond its bounds. The printf statement attempts to print the string starting from the fifth character of the buffer, which is outside the allocated size.

Secure Code

char *buf = malloc(10);
strcpy(buf, "Hello, World!");
printf("%s", buf); // Accessing only within the targeted buffer

This code is secure because it accesses the buffer only within its bounds. The printf statement attempts to print the entire string within the allocated size.

Business Impact of Buffer Over-read

Confidentiality: Buffer Over-read can lead to confidentiality breaches, allowing attackers to read sensitive data such as passwords or credit card numbers.

Integrity: Buffer Over-read can also lead to integrity violations, allowing attackers to modify sensitive data or inject malicious code.

Availability: In some cases, Buffer Over-read can cause denial-of-service attacks, making the application unavailable to users.

Buffer Over-read Attack Scenario

1. The attacker sends a malicious request to the application.
2. The application reads from a buffer using buffer access mechanisms such as indexes or pointers.
3. The buffer is accessed beyond its bounds, allowing the attacker to read sensitive data.
4. The attacker uses the stolen data for malicious purposes.

How to Detect Buffer Over-read

Manual Testing

• Review the code and identify potential buffer over-read vulnerabilities.
• Use tools like Valgrind or AddressSanitizer to detect buffer over-read issues.

Automated Scanners (SAST / DAST)

• Use automated scanners to detect buffer over-read vulnerabilities in your application.
• Contrast what static analysis catches here vs. what needs dynamic/runtime testing to find.

PenScan Detection

• PenScan’s scanner engines actively test for this issue.

False Positive Guidance

• Be cautious of false positives caused by legitimate code patterns that resemble buffer over-read vulnerabilities.

How to Fix Buffer Over-read

• Implement secure coding techniques, such as bounds checking and input validation.
• Use secure programming languages and frameworks that prevent buffer over-read issues.

Framework-Specific Fixes for Buffer Over-read

Java

byte[] buf = new byte[10];
String str = "Hello, World!";
System.arraycopy(str.getBytes(), 0, buf, 0, str.length());
// Accessing only within the targeted buffer

This code is secure because it uses System.arraycopy to copy the string into the buffer, ensuring that the buffer is accessed only within its bounds.

Node.js

const buf = Buffer.alloc(10);
const str = "Hello, World!";
str.copy(buf, 0, 0, str.length());
// Accessing only within the targeted buffer

This code is secure because it uses Buffer.alloc to allocate a buffer and str.copy to copy the string into the buffer, ensuring that the buffer is accessed only within its bounds.

Python/Django

buf = bytearray(10)
str = "Hello, World!"
str.encode(buf[:len(str)])
# Accessing only within the targeted buffer

This code is secure because it uses bytearray to allocate a buffer and encode to copy the string into the buffer, ensuring that the buffer is accessed only within its bounds.

PHP

$buf = str_split("Hello, World!", 10);
// Accessing only within the targeted buffer

This code is secure because it uses str_split to split the string into an array of characters, ensuring that the buffer is accessed only within its bounds.

How to Ask AI to Check Your Code for Buffer Over-read

Review your code with a coding assistant and rewrite it using secure coding techniques, such as bounds checking and input validation. Here’s a sample prompt:

Review the following C++ code block for potential CWE-126 Buffer Over-read vulnerabilities and rewrite it using secure coding techniques:
```c
char *buf = malloc(10);
strcpy(buf, "Hello, World!");
printf("%s", buf + 5); // Accessing memory location after the targeted buffer
```
Rewrite the code to prevent buffer over-read issues.

Buffer Over-read Best Practices Checklist

✅ Validate user input before accessing buffers.

✅ Check buffer sizes and ensure they are large enough to hold the expected data.

✅ Use secure coding techniques, such as bounds checking and input validation.

✅ Avoid using strcpy or other functions that can lead to buffer over-read issues.

Buffer Over-read FAQ

How does Buffer Over-read occur?

Buffer Over-read occurs when an application reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.

What are the common consequences of Buffer Over-read?

The common consequences of Buffer Over-read include confidentiality breaches, integrity violations, and denial-of-service attacks.

How can I detect Buffer Over-read in my application?

You can detect Buffer Over-read using manual testing, automated scanners, or PenScan’s detection capabilities.

What are the best practices for preventing Buffer Over-read?

The best practices for preventing Buffer Over-read include validating user input, checking buffer sizes, and using secure coding techniques.

How can I fix Buffer Over-read in my application?

You can fix Buffer Over-read by implementing secure coding techniques, such as bounds checking and input validation.

What are the related vulnerabilities to Buffer Over-read?

The related vulnerabilities to Buffer Over-read include CWE-125 (Out-of-bounds Read) and CWE-788 (Access of Memory Location After End of Buffer).

How can I use AI to check my code for Buffer Over-read?

You can use AI to check your code for Buffer Over-read by reviewing the code with a coding assistant and rewriting it using secure coding techniques.

What are the best practices for preventing Buffer Over-read in different programming languages?

The best practices for preventing Buffer Over-read in different programming languages include validating user input, checking buffer sizes, and using secure coding techniques specific to each language.

Vulnerabilities Related to Buffer Over-read

References

• MITRE: CWE-126
• 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 Buffer Over-read and other risks before an attacker does.