tun: zero the whole vnet header in tun_put_user()

{
  "id": "fa2740700393714e781025b586f9ce18de700d9e4d20735212da03d94305440b",
  "url": "https://osv.dev/vulnerability/CVE-2026-52940",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "tun: zero the whole vnet header in tun_put_user()",
    "summary": "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.",
    "evidence": "osv:CVE-2026-52940",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.36",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.13",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-52940",
      "aliases": [
        "CVE-2026-52940"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "288f30435132d2f9e7a29ec9b9745a4f9dc7fd37"
                },
                {
                  "fixed": "5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5"
                },
                {
                  "fixed": "585cb85e9a29185be05f326369573c2663cf4380"
                },
                {
                  "fixed": "7f2fcff15e99bb852f6967396ed12b38376e2c8d"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52940.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.17.0"
                },
                {
                  "fixed": "6.18.36"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.0.13"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52940.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:47.024562174Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/585cb85e9a29185be05f326369573c2663cf4380",
        "https://git.kernel.org/stable/c/5fd1fa5a4254bfdd70571c77f5e3bcb4e43738d5",
        "https://git.kernel.org/stable/c/7f2fcff15e99bb852f6967396ed12b38376e2c8d",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52940.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-52940",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52940.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-52940",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 515010,
  "published_at": "2026-06-24T07:14:29.281+00:00"
}