{"id":"CVE-2026-31700","title":"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 buf…","summary":"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 buf…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-362"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 4.6, < 6.6.136","linux_kernel >= 6.7, < 6.12.84","linux_kernel >= 6.13, < 6.18.25","linux_kernel >= 6.19, < 7.0.2","linux_kernel = 7.1"],"patched":["linux_kernel 7.0.2"],"published":"2026-05-01","updated":"2026-09-08","sourceUpdated":"2026-09-08T09:17:59.693","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-31700","references":[{"url":"https://git.kernel.org/stable/c/0f4c9754956b86de158a4af5278c5cf5bda9439e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/1490f82353bdabc09265a74e645b07f05cf4188e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/714aa973da8163925eda7efd49361ccbee21ee46","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00107,"epssPercentile":0.01324,"ingestedAt":"2026-09-08T13:33:23.384Z","slug":"CVE-2026-31700","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `linux_kernel >= 4.6, < 6.6.136`\n- `linux_kernel >= 6.7, < 6.12.84`\n- `linux_kernel >= 6.13, < 6.18.25`\n- `linux_kernel >= 6.19, < 7.0.2`\n- `linux_kernel = 7.1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 7.0.2`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}