CVE-2026-52940: vulnerability in Linux
tun: zero the whole vnet header in tun_put_user()
Published
3Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackepss 0.1%
exploitation probability
0.1%top 99% of all CVEs
observed exploitation
nono source reports it
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 products
Linux · LinuxRelated CVEs — Linux
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