KB5023765: Windows Server 2012 R2 Security Update (March 2023)

An attacker who can reach an RPC endpoint on a Windows Server — and TCP 135 plus the RPC dynamic-port range is reachable internally on virtually every server — can send a crafted RPC request that triggers the integer underflow and runs code in the target service's context. Many RPC servers run as SYSTEM, so the attacker frequently lands with the highest privileges. Mitigation by blocking ports is impractical because RPC is used by so many core Windows features.

Remote Procedure Call (RPC) is one of the most fundamental Windows networking subsystems — used by file sharing, the service control manager, scheduled tasks, AD replication, and dozens of other features. The RPC Runtime is the library that parses incoming RPC requests, and it runs on every Windows machine. An integer-underflow bug in the runtime causes a length calculation to wrap to a very large value, leading to memory corruption when the next operation copies data based on that length.

Probably yes if any of these apply:

A ransomware affiliate inside a corporate network — having phished a single user — discovers that every Windows Server in the environment exposes RPC on TCP 135 and the dynamic high-port range. One crafted RPC request per server, automated across the IP range, gives them SYSTEM on every unpatched host in the network in a single sweep. RPC is the ultimate "everywhere" attack surface.