In part 13 of Web Application Security 101 we cover various business logic security vulnerabilities that effect modern web applications.

1. Business Logic
Vulnerabilities in application-specific features.

2. Examples
Rounding Errors
Number Conversions

3. Rounding Errors
You can see how the type-less systems such as those found in
Python, Ruby, Perl, JavaScript and other could result into a rounding
error.
print 4000/5000
print 4000.0/5000
print round(4000/5000)
print round(4000.0/5000)

4. Number Conversions
Small numbers can be represented in more than one way.
print 0.0005
print 5e-4

5. Lab
Let's discover some business logic flaws.