CVE-2021-26427: Microsoft Exchange Server Remote Code Execution Vulnerability

According to the CVSS, the attack vector is Adjacent. What does that mean and how is that different from a Network vector?

This vulnerability’s attack is limited at the protocol level to a logically adjacent topology. This means it cannot simply be done across the internet, but instead needs something specific tied to the target. Good examples would include the same shared physical network (such as Bluetooth or IEEE 802.11), logical network (local IP subnet), or from within a secure or otherwise limited administrative domain (MPLS, secure VPN to an administrative network zone). This is common to many attacks that require man-in-the-middle type setups or that rely on initially gaining a foothold in another environment.