ZephyrProject Zephyr up to 4.4.1 WireGuard wg_crypto.c wg_process_data_message receiver improper authentication

Summaryinfo

A vulnerability was found in ZephyrProject Zephyr up to 4.4.1 and classified as problematic. This affects the function wg_process_data_message of the file subsys/net/lib/wireguard/wg_crypto.c of the component WireGuard. Such manipulation of the argument receiver leads to improper authentication. This vulnerability is uniquely identified as CVE-2026-13735. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability was found in ZephyrProject Zephyr up to 4.4.1 and classified as problematic. Affected by this issue is the function wg_process_data_message of the file subsys/net/lib/wireguard/wg_crypto.c of the component WireGuard. The manipulation of the argument receiver with an unknown input leads to a improper authentication vulnerability. Using CWE to declare the problem leads to CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Impacted is integrity. CVE summarizes:

Zephyr's WireGuard implementation in subsys/net/lib/wireguard/wg_crypto.c mishandled keepalive packets. In wg_process_data_message(), any type-4 transport-data message whose payload was exactly 16 bytes (an empty plaintext plus a bare Poly1305 tag, i.e. a keepalive) was accepted and returned immediately, before wg_decrypt_packet() was ever called. The Poly1305 authentication tag was therefore never verified; the only preceding gates were a cleartext receiver-index lookup (get_peer_keypair_for_index() on the attacker-supplied data_hdr->receiver) and a non-cryptographic keypair validity/expiry check. The path is reachable entirely from the network: inbound UDP on the WireGuard port is dispatched by wg_input() to handle_transport_data() and then wg_process_data_message(). The 32-bit receiver index is transmitted in cleartext in WireGuard handshake and data messages, so an on-path observer learns it directly and an off-path attacker can brute-force it against the UDP port. Given an active receiving-valid session for that index, an attacker could send a 16-byte garbage payload and have it accepted without possessing the session key. On acceptance the unauthenticated message caused the management layer to observe a spoofed NET_EVENT_VPN_CONNECTED signal (setting peer->first_valid and notifying any net_mgmt listener) and incremented the keepalive-RX statistic. The impact is limited to integrity of this status signal: no plaintext is decrypted or injected, no key is disclosed, and the early-return path did not update the peer endpoint or liveness timers, so there is no traffic-injection, session-takeover, or availability consequence. The fix removes the pre-decrypt early return so a 16-byte payload flows through wg_decrypt_packet(), which verifies the Poly1305 tag over the empty plaintext, followed by the existing anti-replay check; only an authenticated, non-replayed message is then recognised as a keepalive. Forged keepalives now fail the tag check and are counted as decrypt failures.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-13735 since 06/29/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

Upgrading to version 4.4.2 eliminates this vulnerability. Applying the patch 87c520a55f0f0e7cd4adf8780166e45eaad6d81c is able to eliminate this problem.

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Productinfo

Type

• Project Management Software

Vendor

• ZephyrProject

Name

• Zephyr

Version

• 4.4.0
• 4.4.1

CPE 2.3info

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CPE 2.2info

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