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.
Affected versions
Linux kernel versions
6.17
and later are affected. Fixed in
6.18.36,
7.0.13,
7.1
and their respective stable series.
References
3 totalFrequently asked questions
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What is CVE-2026-52940?
CVE-2026-52940 is a unscored severity Linux kernel vulnerability . It affects Linux kernel versions from 6.17 onward and has been patched in 6.18.36, 7.0.13 and 7.1. CVE-2026-52940 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.
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Is there a patch available for CVE-2026-52940?
Yes — CVE-2026-52940 has been patched. Fixed versions include 6.18.36, 7.0.13 and 7.1. If you are running Linux kernel 6.17 or later up to the fix versions, apply the relevant patch for your kernel branch.
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Is CVE-2026-52940 actively exploited?
No — CVE-2026-52940 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.