Abstract. Signature-based input filtering is an important and widely deployed defense. But current signature generation methods have limited coverage and the generated signatures often can be easily evaded by an attacker with small variations of the exploit message. In this paper, we propose protocol-level constraint-guided exploration, a new approach towards generating high coverage vulnerability-based signatures. In particular, our approach generates high coverage, yet compact, vulnerability point reachability predicates, which capture many paths to the vulnerability point. In our experimental results, our tool, Elcano, generates compact, high coverage signatures for real-world vulnerabilities.