CVE-2026-31700 (GCVE-0-2026-31700)

Vulnerability from cvelistv5 – Published: 2026-05-01 13:56 – Updated: 2026-05-03 05:45
VLAI?
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.
Severity ?
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 1d036d25e5609ba73fee6a88db01c306b140d512 , < 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121 (git)
Affected: 1d036d25e5609ba73fee6a88db01c306b140d512 , < 3a1bf9116ea31470b89692585c3910dfe830dcdd (git)
Affected: 1d036d25e5609ba73fee6a88db01c306b140d512 , < 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 (git)
Affected: 1d036d25e5609ba73fee6a88db01c306b140d512 , < 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b (git)
Affected: 1d036d25e5609ba73fee6a88db01c306b140d512 , < 2c054e17d9d41f1020376806c7f750834ced4dc5 (git)
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    Linux Linux Affected: 4.6
Unaffected: 0 , < 4.6 (semver)
Unaffected: 6.6.136 , ≤ 6.6.* (semver)
Unaffected: 6.12.84 , ≤ 6.12.* (semver)
Unaffected: 6.18.25 , ≤ 6.18.* (semver)
Unaffected: 7.0.2 , ≤ 7.0.* (semver)
Unaffected: 7.1-rc1 , ≤ * (original_commit_for_fix)
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}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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