net/packet: fix TOCTOU race on mmap’d vnet_hdr in tpacket_snd()_CVE-2026-31700

{
    "lastseen": "",
    "description": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()\n\nIn tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points\ndirectly into the mmap'd TX ring buffer shared with userspace. The\nkernel validates the header via __packet_snd_vnet_parse() but then\nre-reads all fields later in virtio_net_hdr_to_skb(). A concurrent\nuserspace thread can modify the vnet_hdr fields between validation\nand use, bypassing all safety checks.\n\nThe non-TPACKET path (packet_snd()) already correctly copies vnet_hdr\nto a stack-local variable. All other vnet_hdr consumers in the kernel\n(tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX\npath is the only caller of virtio_net_hdr_to_skb() that reads directly\nfrom user-controlled shared memory.\n\nFix this by copying vnet_hdr from the mmap'd ring buffer to a\nstack-local variable before validation and use, consistent with the\napproach used in packet_snd() and all other callers.",
    "published": "2026-05-01T13:56:00.205Z",
    "modified": "2026-05-03T05:45:25.979Z",
    "type": "cve",
    "title": "net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()",
    "source": "Linux",
    "references": "https://git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121\nhttps://git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd\nhttps://git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27\nhttps://git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b\nhttps://git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5",
    "id": "CVE-2026-31700",
    "bulletinFamily": "",
    "cwe": null,
    "cvelist": null,
    "sourceData": "Linux Linux 1d036d25e5609ba73fee6a88db01c306b140d512\nLinux Linux 1d036d25e5609ba73fee6a88db01c306b140d512\nLinux Linux 1d036d25e5609ba73fee6a88db01c306b140d512\nLinux Linux 1d036d25e5609ba73fee6a88db01c306b140d512\nLinux Linux 1d036d25e5609ba73fee6a88db01c306b140d512\nLinux Linux 4.6",
    "sourceHref": "",
    "cvss": {
        "score": 7.8,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
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            "privilegesRequired": "",
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            "confidentialityImpact": "",
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "Linux",
    "version": "1d036d25e5609ba73fee6a88db01c306b140d512",
    "vendor": "Linux",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}