  With the growth of web applications, REST APIs have become the primary
communication method between services. In order to ensure system reliability
and security, software quality can be assured by effective testing methods.
Black box fuzz testing is one of the effective methods to perform tests on a
large scale. However, conventional black box fuzz testing generates random data
without judging the quality of the input.
  We implement a black box fuzz testing method for REST APIs. It resolves the
issues of blind mutations without knowing the effectiveness by Test Coverage
Level feedback. We also enhance the mutation strategies by reducing the testing
complexity for REST APIs, generating more appropriate test cases to cover
possible paths.
  We evaluate our method by testing two large open-source projects and 89 bugs
are reported and confirmed. In addition, we find 351 bugs from 64 remote API
services in APIs.guru.
  The work is in https://github.com/iasthc/hsuan-fuzz.
