There were supposed to be 14 security bulletins released in this months Patch Tuesday updates. However, it seems only 13 made the grade, leaving many system administrators scratching their head as to whether theyre missing something. Microsoft claims that the vulnerabilities dealt with by the missing security update are not being exploited by hackers at this time. It seems that the missing bulletin failed to adequately pass testing, and has been held back until it’s ready for future release.”]
Source: https://grahamcluley.com/case-missing-microsoft-security-update/