Vulnerability in Linux

CVE-2026-52940

In the Linux kernel, the following vulnerability has been resolved: tun: zero the whole vnet header in tun_put_user() tun_put_user() declares an on-stack struct virtio_net_hdr_v1_hash_tunnel without zeroing it. For a non-tunnel skb, virtio_net_hdr_tnl_from_skb() only initializes the first 10 bytes (sizeof(struct virtio_net_hdr)), leaving bytes 10..23 (num_buffers and the hash/tunnel fields) as stack garbage. An unprivileged user can set the vnet header size to 24 with TUNSETVNETHDRSZ, so __tun_vnet_hdr_put() copies all 24 bytes of the partially-initialized struct to userspace, leaking 14 bytes of kernel stack on every read of a non-tunnel packet. Fix it the same way tun_get_user() already does by zeroing the whole header right after declaration.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.001 (1.3th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 1st percentile — 1.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-52940: held from 0.002 to 0.001.

EPSS over last 30 days · oldest: 0.002 · newest: 0.001 · change: -0.000

Affected products

  • Linux — versions 288f30435132d2f9e7a29ec9b9745a4f9dc7fd37, 6.17, 0
  • Linux Kernel — versions 7.1

References

Frequently asked questions

What is CVE-2026-52940?
CVE-2026-52940 is a medium-severity vulnerability in Linux. CVSS score: 5.5/10. Published 2026-06-24.
How severe is CVE-2026-52940?
Medium severity. CVSS v3 base score is 5.5 out of 10.