CVE-2026-13734 Zephyr WireGuard mutates peer state before anti-replay check, enabling capture-replay endpoint hijack
An attacker can hijack WireGuard peer endpoints and disrupt sessions by replaying captured packets due to premature state mutation before anti-replay checks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-13734?
CVE-2026-13734 is a medium-severity vulnerability in zephyrproject zephyr, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Zephyr's WireGuard VPN data-plane receive handler wg_process_data_message() in subsys/net/lib/wireguard/wg_crypto.c validated the anti-replay counter too late. After AEAD decryption of a MESSAGE_TRANSPORT_DATA packet succeeded, the code committed several peer-state changes — update_peer_addr() (endpoint roaming update), the keypair->last_rx/peer->last_rx liveness timers, and keypair_update() (promote next→current and destroy the previous keypair) — and only afterward called wg_check_replay(). 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 wg_check_replay() to immediately after a successful decrypt, before any peer-state mutation, matching the WireGuard specification and the Linux reference implementation.
Weakness: CWE-294
Which versions are affected by CVE-2026-13734?
How do I fix CVE-2026-13734?
No fix has been published for CVE-2026-13734 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-13734 being exploited?
There is no known exploitation of CVE-2026-13734 in the wild and no public exploit code.
Sources
Also known as GHSA-x7q7-fjx9-4vj2.