For example, by setting certain libcurl options during fuzzer initialization and introducing new seed files, we doubled the line coverage of the HTTP Strict Transport Security (HSTS) handling code and quintupled it for the Alt-Svc header. We also expanded the set of fuzzed protocols to include WebSocket and enabled the fuzzing of many new libcurl options. We’ll conclude this post by explaining some more sophisticated fuzzing techniques the cURL team could adopt to increase coverage even further, bring fuzzing to the cURL command line, and reduce inefficiencies intrinsic to the current test case format.