CVE-2026-80905: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: net: tap: fix wrong transport_header when sending VLAN-tagged frame In tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g. ETH_P_8021Q), skb_set_network_header() is called first to advance network_header past the VLAN tag to the inner protocol header. skb_probe_transport_header() is then called with skb->protocol still set to ETH_P_8021Q, while nhoff (derived from skb_network_offset()) already points past the VLAN tag to the inner protocol header. In __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff points past the VLAN tag. When the dissector hits case ETH_P_8021Q, it reads a struct vlan_hdr at the current nhoff via __skb_header_pointer(), but that offset contains the inner protocol header (e.g. an IP header). The bytes are misinterpreted as a VLAN header, yielding a garbage encapsulated EtherType that matches no known protocol. The dissector returns false, so skb_probe_transport_header() never calls skb_set_transport_header(), leaving transport_header at its uninitialized sentinel value (~0U). Move skb_set_network_header() to after skb_probe_transport_header(). At the time skb_probe_transport_header() is called, network_header still points to the VLAN header (offset ETH_HLEN), so nhoff is correct and the flow dissector can parse the VLAN header, extract the inner EtherType, and advance nhoff to the inner protocol header, allowing transport_header to be set correctly.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 8c76e77f9069f10505c08e02646c3ee11ad79038, < 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b; >= 8c76e77f9069f10505c08e02646c3ee11ad79038, < 88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3; >= 8c76e77f9069f10505c08e02646c3ee11ad79038, < cbb35cbe8db268fefe34c23df15348cf99025298; 3cae5ef1f37a475faf7c40bc6a3c170779f3e0b1; >= 4.20.1, < 4.21
Linux	Linux	5.0

References

Timeline

Published: Sep 4, 2026
Last Modified: Sep 4, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-80905?

In the Linux kernel, the following vulnerability has been resolved: net: tap: fix wrong transport_header when sending VLAN-tagged frame In tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g. ETH_P_8021Q), skb_set_network_header() is called first to advance network_header past the VLAN tag to the inner protocol header. skb_probe_transport_header() is then called with skb->protocol still set to ETH_P_8021Q, while nhoff (derived from skb_network_offset()) already points past the VLAN tag to the inner protocol header. In __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff points past the VLAN tag. When the dissector hits case ETH_P_8021Q, it reads a struct vlan_hdr at the current nhoff via __skb_header_pointer(), but that offset contains the inner protocol header (e.g. an IP header). The bytes are misinterpreted as a VLAN header, yielding a garbage encapsulated EtherType that matches no known protocol. The dissector returns false, so skb_probe_transport_header() never calls skb_set_transport_header(), leaving transport_header at its uninitialized sentinel value (~0U). Move skb_set_network_header() to after skb_probe_transport_header(). At the time skb_probe_transport_header() is called, network_header still points to the VLAN header (offset ETH_HLEN), so nhoff is correct and the flow dissector can parse the VLAN header, extract the inner EtherType, and advance nhoff to the inner protocol header, allowing transport_header to be set correctly.

How severe is CVE-2026-80905?

Severity scoring for CVE-2026-80905 is pending analysis.

How do I fix CVE-2026-80905?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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