Zero-day vulnerabilities have always had something of a special reputation in the cybersecurity space. These software bugs are exploited for attacks before the flaw is known to the software vendor and so before a patch is available. As a result, these security holes are theoretically far harder to defend against and are a more attractive prospect for threat actors. The exploits subsequently devised to take advantage can be a real headache for network defenders. The bad news is that such exploits are now at an all-time high, according to two new pieces of research.