CVE-2026-74684: net: tap: set skb->dev before parsing virtio net header in tap_get_user_xdp()

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-22 · updated 2026-10-30

Description

In the Linux kernel, the following vulnerability has been resolved: net: tap: set skb->dev before parsing virtio net header in tap_get_user_xdp() The commit 4f61f133f354 ("net: tap: NULL pointer derefence in dev_parse_header_protocol when skb->dev is null") fixed a crash in tap_get_user() by assigning skb->dev before calling tun_vnet_hdr_to_skb(). This is required because virtio_net_hdr_to_skb() may invoke dev_parse_header_protocol(), which dereferences skb->dev. Without the assignment, a NULL pointer dereference can occur. However, tap_get_user_xdp() still parses the virtio-net header before assigning skb->dev. When the vhost TX path passes an XDP buffer containing a GSO virtio-net header but the protocol is set to zero on purpose, tun_vnet_hdr_to_skb() can reach dev_parse_header_protocol() while skb->dev is still NULL, resulting in a crash. Fix this by looking up the tap device and assigning skb->dev before calling tun_vnet_hdr_to_skb(), matching the ordering already used in tap_get_user(). Preserve the existing RCU read-side critical section across dev_queue_xmit().

Affected products

Linux: from 4.14.226 before 4.15; from 4.19.181 before 4.20; from 5.4.106 before 5.5; from 5.10.24 before 5.11; from 5.11.7 before 5.12 — fixed in 4.15, 4.20, 5.5, 5.11, 5.12

How to fix

Upgrade to a fixed version: Linux 4.15, 4.20, 5.5, 5.11. Check the vendor advisory for mitigations.

References

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