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

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Summary

CVECVE-2026-31700
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-01 14:16:19 UTC
Updated2026-05-03 07:16:17 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.000180000 probability, percentile 0.048520000 (date 2026-05-02)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 1d036d25e5609ba73fee6a88db01c306b140d512 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121 git Not specified
CNA Linux Linux affected 1d036d25e5609ba73fee6a88db01c306b140d512 3a1bf9116ea31470b89692585c3910dfe830dcdd git Not specified
CNA Linux Linux affected 1d036d25e5609ba73fee6a88db01c306b140d512 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 git Not specified
CNA Linux Linux affected 1d036d25e5609ba73fee6a88db01c306b140d512 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b git Not specified
CNA Linux Linux affected 1d036d25e5609ba73fee6a88db01c306b140d512 2c054e17d9d41f1020376806c7f750834ced4dc5 git Not specified
CNA Linux Linux affected 4.6 Not specified
CNA Linux Linux unaffected 4.6 semver Not specified
CNA Linux Linux unaffected 6.6.136 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.84 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.25 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.2 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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