CVE-2026-11812 UpdateHub: race condition on shared context causes out-of-bounds write and DoS

The UpdateHub management subsystem subsys/mgmt/updatehub/updatehub.c drives every update operation through a single file-scope ctx structure that holds the CoAP block context, payload buffer, status code, socket, and a one-element poll-fd array fds1. Access to ctx was not serialized, and preparef...