WireGuard Kernel Module Silently Overwrites AllowedIPs in Trie, Breaking Peer Routing Without Errors
The WireGuard kernel module stores AllowedIPs in a single prefix trie per device rather than per peer, causing exact-match insertions of identical CIDR prefixes to reassign nodes and remove them from the previous peer's list. This behavior silently drops routing for affected peers while handshakes and inbound traffic continue, leading to one-way connectivity failures and frame errors. The issue affects road-warrior setups using 0.0.0.0/0, mesh networks, Kubernetes CNI plugins such as Cilium and Calico, and network operating systems including VyOS and OPNsense. No warning is emitted by wg, wg-quick, or the kernel on overwrite, and the longest-prefix-match lookup ensures only equal-length prefixes collide. The root cause resides in allowedips.c where rcu_assign_pointer redirects the trie node and list_move_tail detaches it from the original peer. The same logic appears across Linux, wireguard-go, wireguard-nt, FreeBSD, and OpenBSD implementations.
HabrAug 17, 2026Translated from Russian