Systematic Fuzzing and Testing of TLS Libraries

We present TLS-Attacker, an open source framework for evaluating the security of TLS libraries. TLS-Attacker allows security engineers to create custom TLS message flows and arbitrarily modify message contents using a simple interface in order to test the behavior of their libraries. Based on TLS-Attacker, we present a two-stage fuzzing approach to evaluate TLS server behavior. Our approach automatically searches for cryptographic failures and boundary violation vulnerabilities. It allowed us to find unusual padding oracle vulnerabilities and overflows/overreads in widely used TLS libraries, including OpenSSL, Botan, and MatrixSSL. Our findings motivate developers to create comprehensive test suites, including positive as well as negative tests, for the evaluation of TLS libraries. We use TLS-Attacker to create such a test suite framework which finds further problems in Botan.