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CVE-2026-52940

5.5 · MEDIUM

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 with…

Published Jun 24, 2026EPSS 0.11%

Overview

CVE-2026-52940 is a medium-severity vulnerability. It was published on June 24, 2026 and has a CVSS 3.1 base score of 5.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.5, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

Technical description

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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refgit.kernel.org/stable/c/585cb85e9a29185be05f326369573c2663cf4380Refgit.kernel.org/stable/c/5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5Refgit.kernel.org/stable/c/7f2fcff15e99bb852f6967396ed12b38376e2c8d

How CyberStrike helps

Frequently asked questions

What is CVE-2026-52940?

CVE-2026-52940 is a medium-severity vulnerability. It was published on June 24, 2026 and has a CVSS 3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2026-52940?

This vulnerability has a CVSS 3.1 base score of 5.5, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-52940?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-52940?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-52940 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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