net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()
Key facts
- Attack vector
- Local
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 4 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Linux | Linux | 4.6 and later | 5.10.259, 5.15.210, 6.1.176, 6.6.136, 6.12.84, 6.18.25, 7.0.2, 7.1 | Patch available | CNA |
- Linux VendorLinux Affected 4.6 and later Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.136, 6.12.84, 6.18.25, 7.0.2, 7.1 Patch available CNA
CPE configurations NVD · 3
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | 4.6 to before 6.6.136; 6.7 to before 6.12.84; 6.13 to before 6.18.25; 6.19 to before 7.0.2 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* | 7.1 rc1 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* | 7.1 rc2 | Vulnerable | Linux |
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions 4.6 to before 6.6.136; 6.7 to before 6.12.84; 6.13 to before 6.18.25; 6.19 to before 7.0.2 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* Versions 7.1 rc1 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* Versions 7.1 rc2 Vulnerable ·Linux
Remediation
- Fix · CNA Linux (Linux) Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.136, 6.12.84, 6.18.25, 7.0.2, 7.1
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
Not affected: 1 product
- Red Hat Enterprise Linux 7
Timeline
- 2026-10-02 Threatist record created from CVE-2026-31700
- 2026-10-03 Alias added: GHSA-hxpw-4fhf-x5hx
- 2026-10-16 CISA SSVC decision points changed
- 2026-10-19 Weakness changed · CISA ADP
References
Patch 5
- https://git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121
- https://git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd
- https://git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27
- https://git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b
- https://git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5
More Linux Kernel vulnerabilities
- TI-2025-26358 tls: fix handling of zero-length records on the rx_list KEVCVSS 3.1CRITICAL 9.8
- TI-2026-38352 netfilter: bridge: make ebt_snat ARP rewrite writable KEVCVSS 3.1HIGH 8.8
- TI-2013-05264 The (1) get_user and (2) put_user API functions in the Linux kernel before 3.5.5 on the… KEVCVSS 3.1HIGH 8.8
- TI-2022-00125 Integer overflow in kernel KEVCVSS 3.1HIGH 8.4
- TI-2013-01864 The perf_swevent_init function in kernel/events/core.c in the Linux kernel before 3.8.9… KEVCVSS 3.1HIGH 8.4
- TI-2021-05514 Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE KEVCVSS 3.1HIGH 8.3
Sources
- CVE-2026-31700 · CVE Program
- CVE-2026-31700 · NVD
- FIRST EPSS
- GHSA-hxpw-4fhf-x5hx · GitHub Advisory Database · CC BY 4.0
- CVE-2026-31700 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences