CVE-2026-13734: Zephyr WireGuard mutates peer state before anti-replay check, enabling capture-replay endpoint hijack
Zephyr's WireGuard VPN data-plane receive handler wgprocessdatamessage() in subsys/net/lib/wireguard/wgcrypto.c validated the anti-replay counter too late. After AEAD decryption of a MESSAGETRANSPORTDATA packet succeeded, the code committed several peer-state changes — updatepeeraddr() (endpoint roaming update), the keypair->lastrx/peer->lastrx liveness timers, and keypairupdate() (promote next→current and destroy the previous keypair) — and only afterward called wgcheckreplay(). On a replayed packet the replay check returned -EINVAL, but none of the preceding mutations were rolled back.
The AEAD tag authenticates content but not freshness, so a replayed-but-authentic transport packet decrypts correctly. An attacker who captures one valid ciphertext off the wire (an on-path or shared-medium observer) can re-inject it from an arbitrary spoofed source address. Reaching the handler requires no credentials: it is driven directly from inbound UDP datagrams via the dispatch in subsys/net/lib/wireguard/wg.c.
Because the state mutations committed before the replay check, the replay repoints the peer endpoint to the attacker-chosen source address (roaming hijack), redirecting the victim's subsequent outbound tunnel traffic until the legitimate peer's next packet re-corrects it; it also prematurely destroys the previous keypair and refreshes the RX liveness timer. The tunnel payload stays encrypted under the session keypair, so this is an integrity/availability impact (traffic redirection and session disruption), not payload disclosure. The fix moves wgcheckreplay() to immediately after a successful decrypt, before any peer-state mutation, matching the WireGuard specification and the Linux reference implementation.
Affected Software
Event History
Frequently Asked Questions
Does exploitation require WireGuard credentials or an established session with the target?
No. The receive handler is reachable directly through inbound UDP datagrams without credentials. However, the attacker must first capture a valid WireGuard transport-data ciphertext, such as from an on-path position or a shared network medium.
What can an attacker do with a captured packet?
They can replay the authentic packet from an arbitrary spoofed source address. Although the replay is ultimately rejected, peer-state changes made first are not rolled back, including updating the peer endpoint and receive/liveness state.