Five common Web application vulnerabilities

Five common Web application vulnerabilities
Sumit Siddharth, Pratiksha Doshi 2006-04-28

1. Introduction

"No language can prevent insecure code, although there are language features which could aid or hinder a security-conscious developer."
-Chris Shiflett

This article looks at five common Web application attacks, primarily for PHP applications, and then presents a case study of a vulnerable Website that was found through Google and easily exploited. Each of the attacks we'll cover are part of a wide field of study, and readers are advised to follow the references listed in each section for further reading. It is important for Web developers and administrators to have a thorough knowledge of these attacks. It should also be noted that that Web applications can be subjected to many more attacks than just those listed here.

While most of the illustrated examples in this article will discuss PHP coding due to its overwhelming popularity on the Web, the concepts also apply to any programming language. The attacks explained in this article are:

1. Remote code execution
2. SQL injection
3. Format string vulnerabilities
4. Cross Site Scripting (XSS)
5. Username enumeration

Considering the somewhat poor programming approach which leads to these attacks, the article provides some real examples of popular products that have had these same vulnerabilities in the past. Some countermeasures are offered with each example to help prevent future vulnerabilities and subsequent attacks.

This article integrates some of the critical points found in a number of whitepapers and articles on common Web application vulnerabilities. The goal is to provide an overview of these problems within one short article.
2. Vulnerabilities
2.1 Remote code execution
As the name suggests, this vulnerability allows an attacker to run arbitrary, system level code on the vulnerable server and retrieve any desired information contained therein. Improper coding errors lead to this vulnerability.

At times, it is difficult to discover this vulnerability during penetration testing assignments but such problems are often revealed while doing a source code review. However, when testing Web applications is is important to remember that exploitation of this vulnerability can lead to total system compromise with the same rights as the Web server itself.

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