HighFix available

net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via __packet_snd_vnet_parse() but then re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent userspace thread can modify the vnet_hdr fields between validation and use, bypassing all safety checks. The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr to a stack-local variable. All other vnet_hdr consumers in the kernel (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX path is the only caller of virtio_net_hdr_to_skb() that reads directly from user-controlled shared memory. Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.

Products: Kernel
Affected versions: Not specified
Fixed versions: 5.10.259, 5.15.210, 6.1.176, 6.12.84, 6.18.25, 6.6.136, 7.0.2
CVEs: CVE-2026-31700
Confirmed fixed CVEs: Not specified
Updated in this feed: 7 Nov 2026, 13:45 UTC · Revision 1

Source evidence

net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

core-osv · Original source

Published 1 May 2026, 13:56 UTC

osv:CVE-2026-31700

Kernel

Fixed versions: 5.10.259, 5.15.210, 6.1.176, 6.6.136, 6.12.84, 6.18.25, 7.0.2

Complete source record

{
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  "url": "https://osv.dev/vulnerability/CVE-2026-31700",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via __packet_snd_vnet_parse() but then re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent userspace thread can modify the vnet_hdr fields between validation and use, bypassing all safety checks. The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr to a stack-local variable. All other vnet_hdr consumers in the kernel (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX path is the only caller of virtio_net_hdr_to_skb() that reads directly from user-controlled shared memory. Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.",
    "evidence": "osv:CVE-2026-31700",
    "products": [
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      "modified": "2026-10-28T02:30:50.873811831Z",
      "provider": "osv",
      "references": [
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        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
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        "https://git.kernel.org/stable/c/0f4c9754956b86de158a4af5278c5cf5bda9439e",
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        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31700.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31700",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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      "provider_metadata": {
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  "source_id": "core-osv",
  "document_id": 519509,
  "published_at": "2026-05-01T13:56:00.205+00:00"
}