Secure Coding in C and C++

Product Author Bios

Robert Seacord began programming (professionally) for IBM in 1982 and has been programming in C since 1985, and in C++ since 1992. Robert is currently a Senior Vulnerability Analyst with the CERT/Coordination Center at the Software Engineering Institute (SEI). He is coauthor of Building Systems from Commercial Components (Addison-Wesley, 2002) and Modernizing Legacy Systems (Addison-Wesley, 2003). The CERT/CC, among other security-related activities, regularly analyzes software vulnerability reports and assesses the risk to the Internet and other critical infrastructure.

"The security of information systems has not improved at a rate consistent with the growth and sophistication of the attacks being made against them. To address this problem, we must improve the underlying strategies and techniques used to create our systems. Specifically, we must build security in from the start, rather than append it as an afterthought. That's the point of Secure Coding in C and C++. In careful detail, this book shows software developers how to build high-quality systems that are less vulnerable to costly and even catastrophic attack. It's a book that every developer should read before the start of any serious project."
--Frank Abagnale, author, lecturer, and leading consultant on fraud prevention and secure documents

Commonly exploited software vulnerabilities are usually caused by avoidable software defects. Having analyzed nearly 18,000 vulnerability reports over the past ten years, the CERT/Coordination Center (CERT/CC) has determined that a relatively small number of root causes account for most of them. This book identifies and explains these causes and shows the steps that can be taken to prevent exploitation. Moreover, this book encourages programmers to adopt security best practices and develop a security mindset that can help protect software from tomorrow's attacks, not just today's.

Drawing on the CERT/CC's reports and conclusions, Robert Seacord systematically identifies the program errors most likely to lead to security breaches, shows how they can be exploited, reviews the potential consequences, and presents secure alternatives.

Coverage includes technical detail on how to

• Improve the overall security of any C/C++ application
• Thwart buffer overflows and stack-smashing attacks that exploit insecure string manipulation logic
• Avoid vulnerabilities and security flaws resulting from the incorrect use of dynamic memory management functions
• Eliminate integer-related problems: integer overflows, sign errors, and truncation errors
• Correctly use formatted output functions without introducing format-string vulnerabilities
• Avoid I/O vulnerabilities, including race conditions

Secure Coding in C and C++ presents hundreds of examples of secure code, insecure code, and exploits, implemented for Windows and Linux. If you're responsible for creating secure C or C++ software--or for keeping it safe--no other book offers you this much detailed, expert assistance.

Online Sample Chapter

Secure Coding in C and C++: Strings

Table of Contents

Foreword.

Preface.

About the Author.

1. Running with Scissors.

    Gauging the Threat

    Security Concepts

    C and C++

    Development Platforms

    Summary

    Further Reading

2. Strings.

    String Characteristics

    Common String Manipulation Errors

    String Vulnerabilities

    Process Memory Organization

    Stack Smashing

    Code Injection

    Arc Injection

    Mitigation Strategies

    Notable Vulnerabilities

    Summary

    Further Reading

3. Pointer Subterfuge.

    Data Locations

    Function Pointers

    Data Pointers

    Modifying the Instruction Pointer

    Global Offset Table

    The .dtors Section

    Virtual Pointers

    The atexit() and on_exit() Functions

    The longjmp() Function

    Exception Handling

    Mitigation Strategies

    Summary

    Further Reading

4. Dynamic Memory Management.

    Dynamic Memory Management

    Common Dynamic Memory Management Errors

    Doug Lea's Memory Allocator

    RtlHeap

    Mitigation Strategies

    Notable Vulnerabilities

    Summary

    Further Reading

5. Integer Security.

    Integers

    Integer Conversions

    Integer Error Conditions

    Integer Operations

    Vulnerabilities

    Nonexceptional Integer Logic Errors

    Mitigation Strategies

    Notable Vulnerabilities

    Summary

    Further Reading

6. Formatted Output.

    Variadic Functions

    Formatted Output Functions

    Exploiting Formatted Output Functions

    Stack Randomization

    Mitigation Strategies

    Notable Vulnerabilities

    Summary

    Further Reading

7. File I/O.

    Concurrency

    Time of Check, Time of Use

    Files as Locks and File Locking

    File System Exploits

    Mitigation Strategies

    Summary

8. Recommended Practices.

    Secure Software Development Principles

    Systems Quality Requirements Engineering

    Threat Modeling

    Use/Misuse Cases

    Architecture and Design

    Off-the-Shelf Software

    Compiler Checks

    Input Validation

    Data Sanitization

    Static Analysis

    Quality Assurance

    Memory Permissions

    Defense in Depth

    TSP-Secure

    Summary

    Further Reading

References.

Acronyms.

Index.

Preface

The CERT Coordination Center (CERT/CC) was formed by the Defense Advanced Research Projects Agency (DARPA) in November 1988 in response to the Morris worm incident, which brought ten percent of Internet systems to a halt in November 1988. The CERT/CC is located in Pittsburgh, Pennsylvania, at the Software Engineering Institute (SEI), a federally funded research and development center sponsored by the U.S. Department of Defense.

The initial focus of the CERT/CC was incident response and analysis. Incidents include successful attacks such as compromises and denial of service, as well as attack attempts, probes, and scans. Since 1988, the CERT/CC has received more than 22,665 hotline calls reporting computer security incidents or requesting information, and has handled more than 319,992 computer security incidents. The number of incidents reported each year continues to grow.

Responding to incidents, while necessary, is insufficient to secure the Internet and interconnected information systems. Analysis indicates that the majority of incidents are caused by trojans, social engineering, and the exploitation of software vulnerabilities, including software defects, design decisions, configuration decisions, and unexpected interactions between systems. The CERT/CC monitors public sources of vulnerability information and regularly receives reports of vulnerabilities. Since 1995, more than 16,726 vulnerabilities have been reported. When a report is received, the CERT/CC analyzes the potential vulnerability and works with technology producers to inform them of security deficiencies in their products and to facilitate and track their response to those problems.

Similar to incident reports, vulnerability reports continue to grow at an alarming rate. While managing vulnerabilities pushes the process upstream, it is again insufficient to address the issues of Internet and information system security. To address the growing number of both vulnerabilities and incidents, it is increasingly apparent that the problem must be attacked at the source by working to prevent the introduction of software vulnerabilities during software development and ongoing maintenance. Analysis of existing vulnerabilities indicates that a relatively small number of root causes account for the majority of vulnerabilities. The goal of this book is to educate developers about these root causes and the steps that can be taken so that vulnerabilities are not introduced.

Audience

Secure Coding in C and C++ should be useful to anyone involved in the development or maintenance of software in C and C++.

• For a C/C++ programmer, this book will teach you how to identify common programming errors that result in software vulnerabilities, understand how these errors are exploited, and implement a solution in a secure fashion.
• For a software project manager, this book identifies the risks and consequences of software vulnerabilities to guide investments in developing secure software.
• For a computer science student, this book will teach you programming practices that will help you to avoid developing bad habits and enable you to develop secure programs during your professional career.
• For a security analyst, this book provides a detailed description of common vulnerabilities, identifies ways to detect these vulnerabilities, and offers practical avoidance strategies.

Organization and Content

Secure Coding in C and C++ provides practical advice on secure practices in C and C++ programming. Producing secure programs requires secure designs. However, even the best designs can lead to insecure programs if developers are unaware of the many security pitfalls inherent in C and C++ programming. This book provides a detailed explanation of common programming errors in C and C++ and describes how these errors can lead to code that is vulnerable to exploitation. The book concentrates on security issues intrinsic to the C and C++ programming languages and associated libraries. It does not emphasize security issues involving interactions with external systems such as databases and web servers, as these are rich topics on their own. The intent is that this book be useful to anyone involved in developing secure C and C++ programs regardless of the specific application.

Secure Coding in C and C++ is organized around functional capabilities commonly implemented by software engineers that have potential security consequences, such as formatted output and arithmetic operations. Each chapter describes insecure programming practices and common errors that can lead to vulnerabilities, how these programming flaws can be exploited, the potential consequences of exploitation, and secure alternatives. Root causes of software vulnerabilities, such as buffer overflows, integer type range errors, and invalid format strings, are identified and explained where applicable. Strategies for securely implementing functional capabilities are described in each chapter, as well as techniques for discovering vulnerabilities in existing code.

This book contains the following chapters:

• Chapter 1 provides an overview of the problem, introduces security terms and concepts, and provides insight as to why so many vulnerabilities are found in C and C++ programs.
• Chapter 2 describes string manipulation in C and C++, common security flaws, and resulting vulnerabilities including buffer overflow and stack smashing. Both code and arc injection exploits are examined.
• Chapter 3 introduces arbitrary memory write exploits that allows an attacker to write a single address to any location in memory. This chapter describes how these exploits can be used to execute arbitrary code on a compromised machine. Vulnerabilities resulting from arbitrary memory writes are discussed in later chapters.
• Chapter 4 describes dynamic memory management. Dynamically allocated buffer overflows, writing to freed memory, and double-free vulnerabilities are described.
• Chapter 5 covers integral security issues (security issues dealing with integers) including integer overflows, sign errors, and truncation errors.
• Chapter 6 describes the correct and incorrect use of formatted output functions. Both format string and buffer overflows vulnerabilities resulting from the incorrect use of these functions are described.
• Chapter 7 describes common vulnerabilities associated with file I/O including race conditions and time of creation, time of use (TOCTOU) vulnerabilities.
• Chapter 8 recommends specific development practices for improving the overall security of your C / C++ application. These recommendations are in addition to the recommendations included in each chapter for addressing specific vulnerability classes.

Secure Coding in C and C++ contains hundreds of examples of secure and insecure code as well as sample exploits. Almost all of these examples are in C and C++, although comparisons are drawn with other languages. The examples are implemented for Windows and Linux operating systems. Unless otherwise stated, Microsoft Windows examples are compiled using Visual C++ .NET and tested on Windows 2000 Professional platform with an Intel Pentium 4 processor while Linux examples are compiled with GNU gcc/g++ and tested running Red Hat Linux 9 on an Intel Pentium 4 processor.

While the specific examples have typically been compiled and tested in one or more of these environments, vulnerabilities are evaluated to determine whether they are specific to or generalizable across compiler version, operating system, microprocessor, applicable C or C++ standards, little or big endian architectures, and execution stack architecture.

This book focuses on programming flaws in C and C++ that are the most common causes of software vulnerabilities. However, because of size and space constraints, not every potential source of vulnerabilities is covered. Vulnerabilities discussed in the book are also cross-referenced with real-world examples from the US-CERT Vulnerability Notes Database at www.kb.cert.org/vuls/.

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Foreword

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Index

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