Race Condition Affecting linux-qemu-rc package, versions <7.1_rc3-r0


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.01% (3rd percentile)

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  • Snyk IDSNYK-CHAINGUARDLATEST-LINUXQEMURC-16727882
  • published17 May 2026
  • disclosed1 May 2026

Introduced: 1 May 2026

CVE-2026-31700  (opens in a new tab)
CWE-362  (opens in a new tab)

How to fix?

Upgrade Chainguard linux-qemu-rc to version 7.1_rc3-r0 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-qemu-rc package and not the linux-qemu-rc package as distributed by Chainguard. See How to fix? for Chainguard relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1