{"id":"CVE-2026-80905","title":"net: tap: fix wrong transport_header when sending VLAN-tagged frame","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: tap: fix wrong transport_header when sending VLAN-tagged frame\n\nIn tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g.\nETH_P_8021Q), skb_set_network_head…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < c0376820922d255ae1d103c32345a6ec4c3266f7","Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < f1d297cad5c1eacd9fadfd0346ad97405ffbf97c","Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b","Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < 88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3","Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < cbb35cbe8db268fefe34c23df15348cf99025298","Linux 3cae5ef1f37a475faf7c40bc6a3c170779f3e0b1","Linux >= 4.20.1 < 4.21","Linux 5.0"],"published":"2026-09-04","updated":"2026-10-21","sourceUpdated":"2026-10-21T12:47:13.437Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-80905","references":[{"url":"https://git.kernel.org/stable/c/c0376820922d255ae1d103c32345a6ec4c3266f7"},{"url":"https://git.kernel.org/stable/c/f1d297cad5c1eacd9fadfd0346ad97405ffbf97c"},{"url":"https://git.kernel.org/stable/c/5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b"},{"url":"https://git.kernel.org/stable/c/88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3"},{"url":"https://git.kernel.org/stable/c/cbb35cbe8db268fefe34c23df15348cf99025298"}],"tags":["cve.org"],"epss":0.00206,"epssPercentile":0.10075,"ingestedAt":"2026-10-21T12:48:53.748Z","slug":"CVE-2026-80905","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: tap: fix wrong transport_header when sending VLAN-tagged frame\n\nIn tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g.\nETH_P_8021Q), skb_set_network_header() is called first to advance\nnetwork_header past the VLAN tag to the inner protocol header.\nskb_probe_transport_header() is then called with skb->protocol still\nset to ETH_P_8021Q, while nhoff (derived from skb_network_offset())\nalready points past the VLAN tag to the inner protocol header.\n\nIn __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff\npoints past the VLAN tag. When the dissector hits case ETH_P_8021Q, it\nreads a struct vlan_hdr at the current nhoff via __skb_header_pointer(),\nbut that offset contains the inner protocol header (e.g. an IP header).\nThe bytes are misinterpreted as a VLAN header, yielding a garbage\nencapsulated EtherType that matches no known protocol. The dissector\nreturns false, so skb_probe_transport_header() never calls\nskb_set_transport_header(), leaving transport_header at its uninitialized\nsentinel value (~0U).\n\nMove skb_set_network_header() to after skb_probe_transport_header(). At\nthe time skb_probe_transport_header() is called, network_header still\npoints to the VLAN header (offset ETH_HLEN), so nhoff is correct and the\nflow dissector can parse the VLAN header, extract the inner EtherType,\nand advance nhoff to the inner protocol header, allowing transport_header\nto be set correctly.\n\n## Affected\n\n- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < c0376820922d255ae1d103c32345a6ec4c3266f7`\n- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < f1d297cad5c1eacd9fadfd0346ad97405ffbf97c`\n- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b`\n- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < 88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3`\n- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < cbb35cbe8db268fefe34c23df15348cf99025298`\n- `Linux 3cae5ef1f37a475faf7c40bc6a3c170779f3e0b1`\n- `Linux >= 4.20.1 < 4.21`\n- `Linux 5.0`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}