The Wireless Mesh Network (WMN) is ubiquitous emerging broadband wireless network. However, the open wireless medium, multi-hop multi-radio architecture and ad-hoc connectivity amongst end-users are such characteristics which increases the vulnerabilities of WMN towards many passive and active attacks. A secure network ensures the confidentiality, integrity and availability of wireless network. Integrity and availability is compromised by active attacks, while the confidentiality of end-users traffic is compromised by passive attacks. Passive attacks are silent in nature and do not harm the network traffic or normal network operations, therefore very difficult to detect. However, passive attacks lay down a foundation for later launching an active attack. In this article, we discuss the vulnerable features and possible passive threats in WMN along with current security mechanisms as well as future research directions. This article will serve as a baseline guide for the passive security threats and related issues in WMNs
