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CVE-2026-31700— net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于tpacket_snd()中mmap d vnet_hdr存在TOCTOU竞争条件，可能导致并发用户空间线程修改vnet_hdr字段绕过安全检查。

CVSS 7.8 · High EPSS 0.11% · P1

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 1d036d25e5609ba73fee6a88db01c306b140d512< 0f4c9754956b86de158a4af5278c5cf5bda9439e affected
1d036d25e5609ba73fee6a88db01c306b140d512< 714aa973da8163925eda7efd49361ccbee21ee46 affected
1d036d25e5609ba73fee6a88db01c306b140d512< 1490f82353bdabc09265a74e645b07f05cf4188e affected
1d036d25e5609ba73fee6a88db01c306b140d512< 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121 affected
1d036d25e5609ba73fee6a88db01c306b140d512< 3a1bf9116ea31470b89692585c3910dfe830dcdd affected
1d036d25e5609ba73fee6a88db01c306b140d512< 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 affected
1d036d25e5609ba73fee6a88db01c306b140d512< 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b affected
1d036d25e5609ba73fee6a88db01c306b140d512< 2c054e17d9d41f1020376806c7f750834ced4dc5 affected
… +10 more rows
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I. Basic Information for CVE-2026-31700

Vulnerability Information
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Vulnerability Title
net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于tpacket_snd()中mmap d vnet_hdr存在TOCTOU竞争条件，可能导致并发用户空间线程修改vnet_hdr字段绕过安全检查。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 1d036d25e5609ba73fee6a88db01c306b140d512 ~ 0f4c9754956b86de158a4af5278c5cf5bda9439e -
Linux Linux 4.6 -

II. Public POCs for CVE-2026-31700

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III. Intelligence Information for CVE-2026-31700

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Patches & Fixes for CVE-2026-31700 (8)

Same Patch Batch · Linux · 2026-05-01 · 146 CVEs total

CVE-2026-43037 9.8 CRITICAL ip6_tunnel: clear skb2->cb[] in ip4ip6_err()
CVE-2026-31705 9.8 CRITICAL ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment
CVE-2026-43038 9.8 CRITICAL ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()
CVE-2026-43011 9.8 CRITICAL net/x25: Fix potential double free of skb
CVE-2026-31718 9.8 CRITICAL ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger
CVE-2026-43039 9.8 CRITICAL net: ti: icssg-prueth: fix missing data copy and wrong recycle in ZC RX dispatch
CVE-2026-31773 8.8 HIGH Bluetooth: SMP: derive legacy responder STK authentication from MITM state
CVE-2026-43018 8.8 HIGH Bluetooth: hci_event: fix potential UAF in hci_le_remote_conn_param_req_evt
CVE-2026-31706 8.8 HIGH ksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl()
CVE-2026-31709 8.8 HIGH smb: client: validate the whole DACL before rewriting it in cifsacl
CVE-2026-43048 8.8 HIGH HID: core: Mitigate potential OOB by removing bogus memset()
CVE-2026-31717 8.8 HIGH ksmbd: validate owner of durable handle on reconnect
CVE-2026-31739 8.8 HIGH crypto: tegra - Add missing CRYPTO_ALG_ASYNC
CVE-2026-31735 8.8 HIGH iommupt: Fix short gather if the unmap goes into a large mapping
CVE-2026-31712 8.3 HIGH ksmbd: require minimum ACE size in smb_check_perm_dacl()
CVE-2026-31771 8.1 HIGH Bluetooth: hci_event: move wake reason storage into validated event handlers
CVE-2026-31779 8.1 HIGH wifi: iwlwifi: mvm: fix potential out-of-bounds read in iwl_mvm_nd_match_info_handler()
CVE-2026-43051 8.1 HIGH HID: wacom: fix out-of-bounds read in wacom_intuos_bt_irq
CVE-2026-31708 8.1 HIGH smb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path
CVE-2026-43056 7.8 HIGH net: mana: fix use-after-free in add_adev() error path

Showing top 20 of 146 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-31700

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