Web Application Security

Chapter 14. Denial of Service (DoS)

Perhaps one of the most popular types of attacks, and the most widely publicized, is the distributed denial of service (DDoS) attack. This attack is a form of denial of service (DoS), in which a large network of devices flood a server with requests, slowing down the server or rendering it unusable for legitimate users.

DoS attacks come in many forms, from the well-known distributed version that involves thousands or more coordinated devices, to code-level DoS that affects a single user as a result of a faulty regex implementation, resulting in long times to validate a string of text. DoS attacks also range in seriousness from reducing an active server, to a functionless electric bill, to causing a user’s web page to load slightly slower than usual or pausing their video midbuffer.

Because of this, it is very difficult to test for DoS attacks (in particular, the less severe ones). Most bug bounty programs outright ban DoS submissions to prevent bounty hunters from interfering with regular application usage.

Warning

Because DoS vulnerabilities interfere with the usage of normal users via the application, it is most effective to test for DoS vulnerabilities in a local development environment where real users will not experience service interruption.

Except for a few exceptions, DoS attacks usually do not cause permanent damage to an application, but do interfere with the usability of an application for legitimate users. Depending on the specific ...