Dynamic concolic execution of an application. A first hypotheses pertaining to a nature of test payloads that satisfy a specified property, and that are expected to satisfy a condition tested by the application's program code, can be generated. A plurality of first test payloads to test first hypothesis can be synthesized and submitted to the application during respective executions of the application. Whether each of the first test payloads actually satisfy the condition tested by the application's program code can be determined. When at least one of the first test payloads does not actually satisfy the condition tested by the application's program code, a second hypotheses that is expected to satisfy the condition tested by the application's program code can be generated. A plurality of second test payloads to test the second hypothesis can be synthesized and submitted to the application during respective executions of the application.