CVE-2026-19673 Out-of-bounds read and net_buf length underflow in Zephyr Ethernet L2 when parsing a truncated VLAN header
Remote attackers can cause denial of service and potential information disclosure in Zephyr RTOS by sending truncated VLAN frames to interfaces with VLAN enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-19673?
CVE-2026-19673 is a high-severity vulnerability in zephyrproject zephyr, published on 14 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
ethernet_recv() in subsys/net/l2/ethernet/ethernet.c validates only that the first net_buf of a received frame holds a plain 14-byte struct net_eth_hdr. When the ethertype is 0x8100 and VLAN is enabled on the interface, the same buffer is reinterpreted as the 18-byte struct net_eth_vlan_hdr without re-checking the length: the VLAN TCI and the inner ethertype are read from offsets 14..17, past pkt->buffer->len, and hdr_len is raised to 18 so the subsequent net_buf_pull() removes more bytes than the buffer holds.
A single unauthenticated frame of 14 to 17 bytes carrying the VLAN ethertype triggers this. No knowledge of the node's VLAN configuration is needed: net_eth_get_vlan_iface() returns the base interface for the priority tag 0, and a broadcast destination address satisfies the "frame is for me" test, so a 16-byte broadcast frame with ethertype 0x8100 and TCI 0x0000 reaches the pull. Nothing in the receive path enforces the 60-byte Ethernet minimum — the USB CDC ECM and CDC NCM gadget classes in particular hand host-supplied frames of any non-zero length straight to net_recv_data().
With assertions enabled, net_buf_simple_pull() asserts and the node panics. In a production build (assertions and CONFIG_NET_BUF_HARDENING off) the uint16_t buffer length underflows to 65534 and buf->data is advanced past the end of the fragment's storage, so every later parser reads far outside the buffer and any net_buf_add() on that fragment computes tailroom from the underflowed length. The result is a reliable remote denial of service and out-of-bounds access with information-disclosure and corruption potential.
Only configurations built with CONFIG_NET_VLAN=y that have a VLAN enabled on the receiving Ethernet interface, and whose MAC does not strip VLAN tags in hardware (ETHERNET_HW_VLAN_TAG_STRIP), are affected. The fix rejects the frame before the tag is read, so hdr_len is thereafter either 14 or 18 with both sizes validated against pkt->buffer->len.
Weakness: CWE-125
Which versions are affected by CVE-2026-19673?
How do I fix CVE-2026-19673?
No fix has been published for CVE-2026-19673 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19673 being exploited?
There is no known exploitation of CVE-2026-19673 in the wild and no public exploit code.
Sources
Also known as GHSA-79rf-rwff-f4vg.