CVE-2026-31700 — net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.1% (30-day exploitation probability)+0
- Technical severity (high)+6
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes matching the vulnerability class (logic error), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux |
≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 0f4c9754956b86de158a4af5278c5cf5bda9439e≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 714aa973da8163925eda7efd49361ccbee21ee46≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 1490f82353bdabc09265a74e645b07f05cf4188e≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 3a1bf9116ea31470b89692585c3910dfe830dcdd≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b≥ 1d036d25e5609ba73fee6a88db01c306b140d512 and < 2c054e17d9d41f1020376806c7f750834ced4dc5 and 1 moreversion 4.6 |
Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel | ≥ 4.6 and < 6.6.136≥ 6.7 and < 6.12.84≥ 6.13 and < 6.18.25≥ 6.19 and < 7.0.2version 7.1-rc1version 7.1-rc2 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.8 | CVSS 3.1 | High | 1.8 | 5.9 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database |
| 7.8 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
| 7.8 | CVSS 3.1 | High | — | — | Linux via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.15%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- Fix documented
- CVSS changed · 7.8
- Source status changed · → Modified
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
13 on the record
- git.kernel.org/stable/c/48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b
- git.kernel.org/stable/c/74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121
- git.kernel.org/stable/c/28324a3b62d9ce7f9bdd65a8ce63f382041d1b27
- git.kernel.org/stable/c/3a1bf9116ea31470b89692585c3910dfe830dcdd
- git.kernel.org/stable/c/2c054e17d9d41f1020376806c7f750834ced4dc5
- nvd.nist.gov/vuln/detail/CVE-2026-31700
- git.kernel.org/stable/c/0f4c9754956b86de158a4af5278c5cf5bda9439e
- git.kernel.org/stable/c/1490f82353bdabc09265a74e645b07f05cf4188e
- cert-portal.siemens.com/productcert/html/ssa-457936.html
- git.kernel.org/stable/c/714aa973da8163925eda7efd49361ccbee21ee46
- cert-portal.siemens.com/productcert/html/ssa-019113.html
- github.com/advisories/GHSA-hxpw-4fhf-x5hx
- cert-portal.siemens.com/productcert/html/ssa-784472.html
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 12h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 12h
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
- Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CISA SSVC assessment.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-31700 is "net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()", rated High. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.8 describes technical severity. EPSS 0.11% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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