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CVE-2026-31684 is a nested VLAN header validation vulnerability in the Linux kernel network scheduler's act_csum checksum action. When a socket buffer retains in-payload VLAN tags, tcf_csum_act() reads vlan->h_vlan_encapsulated_proto and removes VLAN_HLEN bytes without first checking that a complete header is present in the buffer's linear area. A partially linearized inner VLAN header can consequently cause an out-of-bounds read, while the subsequent skb_pull(VLAN_HLEN) operation may violate socket-buffer invariants. Specially crafted packets can trigger kernel instability, a system crash, and denial of service.
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A Linux kernel networking vulnerability involving nested VLAN header validation in the act_csum traffic-control action. Security updates are available for affected Rocky Linux 10.2 kernel packages.
A Linux kernel flaw in tcf_csum_act() allows nested VLAN headers to be accessed and removed without verifying that the complete header is present in the socket buffer's linear area. This can cause an out-of-bounds read and violate buffer invariants, potentially affecting availability. The reference assigns a CVSS v3 base score of 5.5, with local access and low privileges required. The fix checks each nested header using pskb_may_pull() and drops packets with incomplete headers.
A Linux kernel vulnerability in net/sched/act_csum involving validation of nested VLAN headers, fixed by this Red Hat kernel update.
A Linux kernel networking vulnerability in net sched act_csum related to validation of nested VLAN headers.
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