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NVD / CVE Program· CNA Linux

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

Noroxi assessment

Priority: Monitor (action score 31/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.11% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 0f4c9754956b86de158a4af5278c5cf5bda9439e, 1490f82353bdabc09265a74e645b07f05cf4188e, 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27; azl3 kernel 6.6.134.1-2 on Azure Linux 3.0 6.6.137.1-2.

Low priority for now. Upgrade to Linux Linux 0f4c9754956b86de158a4af5278c5cf5bda9439e, 1490f82353bdabc09265a74e645b07f05cf4188e, 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27; azl3 kernel 6.6.134.1-2 on Azure Linux 3.0 6.6.137.1-2 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
May 1, 2026
Updated
Oct 19, 2026
EPSS
0.1% · 1th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
7.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-31700

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel4.6 and later · before 6.6.136
  • linux linux kernel6.7 and later · before 6.12.84
  • linux linux kernel6.13 and later · before 6.18.25
  • linux linux kernel6.19 and later · before 7.0.2
  • linux linux kernel7.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 4.6affected
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 0f4c9754956b86de158a4af5278c5cf5bda9439eaffected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 714aa973da8163925eda7efd49361ccbee21ee46affected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 1490f82353bdabc09265a74e645b07f05cf4188eaffected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121affected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 3a1bf9116ea31470b89692585c3910dfe830dcddaffected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27affected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804baffected · git
    • 1d036d25e5609ba73fee6a88db01c306b140d512 and later · before 2c054e17d9d41f1020376806c7f750834ced4dc5affected · git
    • before 4.6not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.176-16.1.176-1
Debian:13linuxbefore 6.12.85-16.12.85-1
Debian:14linuxbefore 7.0.3-17.0.3-1
openSUSE:Tumbleweedkernel-sourcebefore 7.0.7-1.17.0.7-1.1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-31698May 1, 2026 · crypto: ccp: Don't attempt to copy PDH cert to userspace if PSP command failed
    28Monitor
  • ← EarlierCVE-2026-31699May 1, 2026 · crypto: ccp: Don't attempt to copy CSR to userspace if PSP command failed
    28Monitor
  • Later →CVE-2026-31704May 1, 2026 · ksmbd: use check_add_overflow() to prevent u16 DACL size overflow
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux0f4c9754956b86de158a4af5278c5cf5bda9439eVendor (CNA)
Linux Linux1490f82353bdabc09265a74e645b07f05cf4188eVendor (CNA)
Linux Linux28324a3b62d9ce7f9bdd65a8ce63f382041d1b27Vendor (CNA)
Linux Linux2c054e17d9d41f1020376806c7f750834ced4dc5Vendor (CNA)
Linux Linux3a1bf9116ea31470b89692585c3910dfe830dcddVendor (CNA)
Linux Linux48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804bVendor (CNA)
Linux Linux714aa973da8163925eda7efd49361ccbee21ee46Vendor (CNA)
Linux Linux74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121Vendor (CNA)
azl3 kernel 6.6.134.1-2 on Azure Linux 3.06.6.137.1-2 · CBL-Mariner ReleasesMicrosoft (MSRC)
debian:linux6.1.176-1 · Debian:12Package registry (OSV)
opensuse:kernel-source7.0.7-1.1 · openSUSE:TumbleweedPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (10 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records