Preventing Web Attacks with Apache

About the Author xix

Foreword xxi

Acknowledgments xxv

Introduction xxvii

Chapter 1 Web Insecurity Contributing Factors 1

A Typical Morning 1

Why Web Security Is Important 3

Web Insecurity Contributing Factors 4

Managerial/Procedural Issues 4

Management and the Bottom Line 4

Selling Loaded Guns 5

The Two-Minute Drill 5

Development Environment Versus Production Environment 6

Firefighting Approach to Web Security (Reacting to Fires) 7

Technical Misconceptions Regarding Web Security 7

"We have our web server in a Demilitarized Zone (DMZ)." 8

"We have a firewall." 9

"We have a Network-Based Intrusion Detection System." 9

"We have a Host-Based Intrusion Detection System." 11

"We are using Secure Socket Layer (SSL)." 11

Summary 11

Chapter 2 CIS Apache Benchmark 13

CIS Apache Benchmark for UNIX: OS-Level Issues 13

Minimize/Patch Non-HTTP Services 13

Example Service Attack: 7350wu-FTP Exploit 19

Vulnerable Services' Impact on Apache's Security 22

Apply Vendor OS Patches 23

Tune the IP Stack 24

Denial of Service Attacks 25

Create the Web Groups and User Account 28

Lock Down the Web Server User Account 31

Implementing Disk Quotas 32

Accessing OS-Level Commands 35

Update the Ownership and Permissions of System Commands 39

Traditional Chroot 40

Chroot Setup Warning 41

Mod_Security Chroot 41

Chroot Setup 41

Summary 50

Chapter 3 Downloading and Installing Apache 53

Apache 1.3 Versus 2.0 53

Using Pre-Compiled Binary Versus Source Code 54

Downloading the Apache Source Code 56

Why Verify with MD5 and PGP? 56

Uncompress and Open: Gunzip and Untar 63

Patches-Get 'em While They're Hot! 64

Monitoring for Vulnerabilities and Patches 66

What Modules Should I Use? 70

Summary 80

Chapter 4 Configuring the httpd.conf File 81

CIS Apache Benchmark Settings 84

The httpd.conf File 85

Disable Un-Needed Modules 86

Directives 86

Server-Oriented Directives 87

Multi-Processing Modules (MPMs) 87

Listen 88

ServerName 88

ServerRoot 89

DocumentRoot 89

HostnameLookups 89

User-Oriented Directives 90

User 90

Group 91

ServerAdmin 91

Denial of Service (DoS) Protective Directives 92

Testing with Apache HTTP Server Benchmarking Tool (ab) in Default Configuration 92

TimeOut 94

KeepAlive 95

KeepAliveTimeout 95

MaxKeepAliveRequests 95

StartServers 96

MinSpareServers and MaxSpareServers 96

ListenBacklog 96

MaxClients and ServerLimit 97

Testing with Apache HTTP Benchmarking Tool (ab) with Updated Configuration 97

Forward Reference 99

Software Obfuscation Directives 99

ServerTokens 99

ServerSignature 101

ErrorDocument 102

Directory Functionality Directives 104

All 104

ExecCGI 104

FollowSymLinks and SymLinksIfOwnerMatch 105

Includes and IncludesNoExec 105

Indexes 106

AllowOverride 106

Multiviews 107

Access Control Directives 107

Authentication Setup 108

Authorization 109

Order 110

Order deny, allow 110

Order allow, deny 110

Access Control: Where Clients Come From 111

Hostname or Domain 111

IP Address and IP Range 112

Client Request ENV 112

Protecting the Root Directory 113

Limiting HTTP Request Methods 114

Logging General Directives 114

LogLevel 114

ErrorLog 115

LogFormat 115

CustomLog 115

Removing Default/Sample Files 116

Apache Source Code Files 116

Default HTML Files 116

Sample CGIs 117

Webserv User Files 118

Updating Ownership and Permissions 118

Server Configuration Files 119

DocumentRoot Files 119

CGI-Bin 119

Logs 120

Bin 120

Updating the Apachectl Script 120

Nikto Scan After Updates 122

Summary 122

Chapter 5 Essential Security Modules for Apache 125

Secure Socket Layer (SSL) 125

Why Should I Use SSL? 126

How Does SSL Work? 128

Software Requirements 132

Installing SSL 133

Creating an SSL Certificate 133

Testing the Initial Configuration 134

Configuring mod_ssl 137

SSL Summary 144

Mod_Rewrite 144

Enabling Mod_Rewrite 145

Mod_Rewrite Summary 147

Mod_Log_Forensic 147

Mod_Dosevasive 149

What Is Mod_Dosevasive? 149

Installing Mod_Dosevasive 149

How Does Mod_Dosevasive Work? 150

Configuration 151

Mod_Dosevasive Summary 155

Mod_Security 155

Installing Mod_Security 156

Mod_Security Overview 156

Features and Capabilities of Mod_Security 157

Anti-Evasion Techniques 158

Special Built-In Checks 159

Filtering Rules 162

Actions 164

Wait, There's Even More! 168

Summary 169

Chapter 6 Using the Center for Internet Security Apache Benchmark Scoring Tool 171

Downloading, Unpacking, and Running the Scoring Tool 171

Unpacking the Archive 173

Running the Tool 174

Summary 180

Chapter 7 Mitigating the WASC Web Security Threat Classification with Apache 181

Contributors 182

Web Security Threat Classification Description 182

Goals 183

Documentation Uses 183

Overview 183

Background 184

Classes of Attack 184

Threat Format 186

Authentication 186

Brute Force 187

Insufficient Authentication 191

Weak Password Recovery Validation 192

Authorization 195

Credential/Session Prediction 195

Insufficient Authorization 198

Insufficient Session Expiration 199

Session Fixation 201

Client-Side Attacks 205

Content Spoofing 205

Cross-Site Scripting 207

Command Execution 210

Buffer Overflow 210

Format String Attack 215

LDAP Injection 218

OS Commanding 220

SQL Injection 223

SSI Injection 228

XPath Injection 230

Information Disclosure 232

Directory Indexing 232

Information Leakage 236

Path Traversal 239

Predictable Resource Location 242

Logical Attacks 243

Abuse of Functionality 244

Denial of Service 246

Insufficient Anti-Automation 250

Insufficient Process Validation 251

Summary 253

Chapter 8 Protecting a Flawed Web Application: Buggy Bank 255

Installing Buggy Bank 256

Buggy Bank Files 257

Turn Off Security Settings 258

Testing the Installation 258

Functionality 261

Login Accounts 262

Assessment Methodology 262

General Questions 262

Tools Used 263

Configuring Burp Proxy 263

Buggy Bank Vulnerabilities 266

Comments in HTML 266

Enumerating Account Numbers 267

How Much Entropy? 270

Brute Forcing the Account Numbers 270

Enumerating PIN Numbers 273

Account Unlocked 274

Account Locked 274

Brute Forcing the PIN Numbers 276

Command Injection 277

Injecting Netstat 278

SQL Injection 282

SQL Injection Mitigation 285

Cross-Site Scripting (XSS) 287

Mitigations 289

Balance Transfer Logic Flaw 290

Mitigation 292

Summary 293

Chapter 9 Prevention and Countermeasures 295

Why Firewalls Fail to Protect Web Servers/Applications 296

Why Intrusion Detection Systems Fail as Well 299

Deep Packet Inspection Firewalls, Inline IDS, and Web Application Firewalls 304

Deep Packet Inspection Firewall 304

Inline IDS 305

Web Application Firewall (WAF) 307

Web Intrusion Detection Concepts 309

Signature-Based 309

Positive Policy Enforcement (White-Listing) 314

Header-Based Inspection 325

Protocol-Based Inspection 329

Uniform Resource Identifier (URI) Inspection 336

Heuristic-Based Inspection 339

Anomaly-Based Inspection 340

Web IDS Evasion Techniques and Countermeasures 342

HTTP IDS Evasion Options 342

Anti-Evasion Mechanisms 347

Evasion by Abusing Apache Functionality 348

Identifying Probes and Blocking Well-Known Offenders 352

Worm Probes 352

Blocking Well-Known Offenders 354

Nmap Ident Scan 357

Nmap Version Scanning 358

Why Change the Server Banner Information? 359

Masking the Server Banner Information 361

HTTP Fingerprinting 363

Implementation Differences of the HTTP Protocol 364

Banner Grabbing 370

Advanced Web Server Fingerprinting 370

HTTPrint 371

Web Server Fingerprinting Defensive Recommendations 373

Bad Bots, Curious Clients, and Super Scanners 379

Bad Bots and Curious Clients 379

Super Scanners 381

Reacting to DoS, Brute Force, and Web Defacement Attacks 388

DoS Attacks 388

Brute Force Attacks 389

Web Defacements 392

Defacement Countermeasures 397

Alert Notification and Tracking Attackers 399

Setting Up Variables 402

Creating Historical Knowledge 403

Filtering Out Noise and Thresholding Emails 403

Request Snapshot and Attacker Tracking Links 403

Send Alert to Pager 404

Crude Pause Feature 404

Send the HTML 404

Example Email Alerts 404

Log Monitoring and Analysis 412

Real-Time Monitoring with SWATCH 413

Heuristic/Statistical Log Monitoring with SIDS 417

Honeypot Options 424

Sticky Honeypot 424

Fake PHF 425

OS Commanding Trap and Trace 427

Mod_Rewrite (2.1) to the Rescue 428

Summary 429

Chapter 10 Open Web Proxy Honeypot 431

Why Deploy an Open Web Proxy Honeypot? 431

Lack of Knowledge That an Attack Even Occurred 432

Lack of Verbose/Adequate Logging of HTTP Transactions 432

Lack of Interest in Public Disclosure of the Attack 432

What Are Proxy Servers? 433

Open Proxy Background 434

Open Web Proxy Honeypot 435

Linksys Router/Firewall 435

Turn Off Un-Needed Network Services 436

Configure Apache for Proxy 436

Data Control 439

Mod_Dosevasive 439

Mod_Security 439

Utilizing Snort Signatures 441

Brute Force Attacks 441

Data Capture 442

Real-Time Monitoring with Webspy 444

Honeynet Project's Scan of the Month Challenge #31 444

The Challenge 445

Initial Steps 446

Question: How Do You Think the Attackers Found the Honeyproxy? 447

Question: What Different Types of Attacks Can You Identify? For Each Category, Provide Just One Log Example and Detail as Much Info About the Attack as Possible (Such as CERT/CVE/Anti-Virus ID Numbers). How Many Can You Find? 448

Search Logs for Mod_Security-Message 449

Utilization of the AllowCONNECT Proxying Capabilities 450

Search Logs for Abnormal HTTP Status Codes 451

Abnormal HTTP Request Methods 454

Non-HTTP Compliant Requests 455

Attack Category-SPAMMERS 457

Attack Category-Brute Force Authentication 459

Attack Category-Vulnerability Scans 459

Attack Category-Web-Based Worms 465

Attack Category-Banner/Click-Thru Fraud 468

Attack Category-IRC Connections 469

Question: Do Attackers Target Secure Socket Layer (SSL)-Enabled Web Servers? 470

Did They Target SSL on Our Honeyproxy? 471

Why Would They Want to Use SSL? 472

Why Didn't They Use SSL Exclusively? 472

Question: Are There Any Indications of Attackers Chaining Through Other Proxy Servers? Describe How You Identified This Activity. List Other Proxy Servers Identified. Can You Confirm That These Are Indeed Proxy Servers? 473

Identifying the Activity 473

Confirming the Proxy Servers 475

Targeting Specific Open Proxies 479

Targeting Specific Destination Servers 480

Question: Identify the Different Brute Force Authentication Attack Methods. Can You Obtain the Clear-Text Username/Password Credentials? Describe Your Methods. 481

HTTP GET Requests 481

HTTP POST Requests 482

HTTP Basic Authentication 483

Obtaining the Cleartext Authorization Credentials 485

Distributed Brute Force Scan Against Yahoo Accounts 486

Forward and Reverse Scanning 487

Question: What Does the Mod_Security Error Message "Invalid Character Detected" Mean? What Were the Attackers Trying to Accomplish? 493

SecFilterCheckURLEncoding-URL-Encoding Validation 493

SecFilterCheckUnicodeEncoding-Unicode-Encoding Validation 494

SecFilterForceByteRange-Byte Range Check 494

SOCKS Proxy Scan 494

Code Red/NIMDA Worm Attacks 495

Question: Several Attackers Tried to Send SPAM by Accessing the Following URL: http://mail.sina.com.cn/cgi-bin/sendmsg.cgi. They Tried to Send Email with an HTML Attachment (Files Listed in the /upload Directory). What Does the SPAM Web Page Say? Who Are the SPAM Recipients? 496

SPAM Recipients 497

Question: Provide Some High-Level Statistics. 498

Top Ten Attacker IP Addresses 498

Top Ten Targets 500

Top User-Agents (Any Weird/Fake Agent Strings?) 500

Attacker Correlation from DShield and Other Sources? 501

Bonus Question: Why Do You Think the Attackers Were Targeting Pornography Web sites for Brute Force Attacks? (Besides the Obvious Physical Gratification Scenarios.) 502

Even Though the Proxypot's IP/Hostname Was Obfuscated from the Logs, Can You Still Determine the Probable Network Block Owner? 504

Summary 506

Chapter 11 Putting It All Together 509

Example Vulnerability Alert 509

Verify the Software Version 510

Patch Availability 510

Vulnerability Details 511

Creating a Mod_Security Vulnerability Filter 514

Testing the Vulnerability Filter 515

First Aid Versus a Hospital 516

Web Security: Beyond the Web Server 517

Domain Hijacking 517

DNS Cache Poisoning 517

Caching Proxy Defacement 519

Banner Ad Defacement 520

News Ticker Manipulations 521

Defacement or No Defacement? 521

Summary 522

Appendix A Web Application Security Consortium Glossary 523

Appendix B Apache Module Listing 533

Appendix C Example httpd.conf File 549

Index 561