CVE-2026-79977
HighCVSS 8.2Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
A vulnerability in the WireGuard service in Zephyr RTOS (subsys/net/lib/wireguard/wg.c) allows the peer endpoint to be updated from an unauthenticated transport-data message. In handle_transport_data(), when the 32-bit receiver index matches no session, the code copies the datagram's source address into peer->endpoint even though no key exists to verify the message. A single spoofed UDP datagram sent to port 51820 can persistently redirect tunnel traffic to an attacker-chosen address.
Risk Assessment
An attacker with network access to UDP port 51820 can remotely and without authentication redirect the peer endpoint, causing persistent tunnel unavailability (loss of connectivity) and enabling on-path relay to observe traffic metadata. WireGuard's end-to-end cryptography still prevents decryption or forgery of tunnel content, so keys are not compromised.
Recommendation
Update Zephyr to a version containing the fix that removes endpoint learning from the unauthenticated path and sends handshakes only to an authenticated or configured endpoint (cfg_endpoint). Until patched, consider disabling CONFIG_WIREGUARD or restricting access to UDP port 51820 via firewall rules.
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Original NVD description (English source)
The WireGuard VPN service in subsys/net/lib/wireguard/wg.c updated the peer endpoint from a message it could not authenticate. In handle_transport_data(), when the 32-bit receiver index of an incoming transport-data message matched no session, the code both scheduled a new handshake and copied the datagram's source address into peer->endpoint with memcpy(&peer->endpoint, peer_addr, sizeof(peer->endpoint)). Because the receiver index is unknown, there is no key with which such a message could be verified, so the address written into peer->endpoint is entirely attacker-supplied. Every other endpoint update in the implementation happens only after authentication — after the Noise handshake in handle_handshake_init(), or after AEAD decryption plus the anti-replay check in wg_process_data_message(). The WireGuard listener is registered with net_udp_register() using no remote address or port filter and defaults to UDP port 51820 (CONFIG_WIREGUARD_PORT), and wg_ctrl_recv() resolves the peer by interface rather than by any cryptographic identity. Any host able to send a UDP datagram to that port can therefore reach the defect off-path, with no need to observe legitimate traffic: a 16-byte datagram carrying the transport-data type, zeroed reserved bytes and an arbitrary receiver index is sufficient. The vulnerable branch runs whenever the peer has neither a valid handshake nor a current keypair — the state at boot and after a session expires. A single spoofed datagram redirects peer->endpoint to an address of the attacker's choosing, and all subsequent handshake initiations, keepalives and encrypted data packets are sent there. The legitimate peer never receives the initiations and so never re-authenticates, and nothing resets the endpoint afterwards, leaving the tunnel persistently unusable on devices whose peer does not initiate handshakes itself. The attacker can also relay the redirected initiations to the real peer to place itself in the path of the tunnel, observing ciphertext and traffic metadata and selectively dropping packets. WireGuard's end-to-end cryptography still prevents decryption or forgery of tunnel content, so the impact is loss of availability plus limited confidentiality, not key compromise. The fix removes the endpoint learning from this path entirely: the stale-session recovery is kept, but the handshake is sent only to an endpoint learnt from an authenticated message, falling back to the configured cfg_endpoint, and the message is dropped when neither is known. CONFIG_WIREGUARD is marked experimental and is not enabled by default.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS