CVE-2026-10653 Non-atomic `net_buf` reference counts cause double-free / free-list corruption under concurrent unref

The Zephyr netbuf library lib/netbuf/buf.c manipulated both of its reference counts -- the per-header buf-ref and the per-data-block refcount at the start of each variable/heap data allocation -- with plain non-atomic C operators buf-ref++, if --buf-ref 0, if --refcount. The API is documented as...

CVE-2026-10653

The CVE-2026-10653 issue affects the Zephyr net_buf library (lib/net_buf/buf.c). It relies on non-atomic operations for two reference counters: the per-header buf->ref and the per-data-block ref_count. Under true concurrency, two independent unrefs can observe the same prior value and both tre...