CVE-2026-31700

Description

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.

Is your site exposed to CVE-2026-31700?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

7.8

HIGH

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

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.02%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-362 CWE-362

Affected Products

Vendor	Product	Versions
linux	linux_kernel	4.6 — 6.6.136
linux	linux_kernel	6.7 — 6.12.84
linux	linux_kernel	6.13 — 6.18.25
linux	linux_kernel	6.19 — 7.0.2
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 https://git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5 https://git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd https://git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b https://git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121

Frequently Asked Questions

What is CVE-2026-31700? +

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. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2026-31700? +

CVE-2026-31700 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-31700? +

CVE-2026-31700 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-31700? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-41458

OwnTone Server versions 28.4 through 29.0 contain a race condition vulnerability in the DAAP login handler that allows unauthenticated attackers …

CVE-2025-13036

An authentication bypass security issue exists within FactoryTalk Historian Site Edition. By continually sending requests to the login endpoint, an …

CVE-2025-0372

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') vulnerability in HYPR Passwordless on Windows allows Privilege Escalation.This issue …

CVE-2025-59052

Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages. Angular uses a …

CVE-2024-47534

go-tuf is a Go implementation of The Update Framework (TUF). The go-tuf client inconsistently traces the delegations. For example, if …

CVE-2025-64118

node-tar is a Tar for Node.js. In 7.5.1, using .t (aka .list) with { sync: true } to read tar …