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NVD / CVE Program· CNA Linux

CVE-2026-63867: mptcp: close TOCTOU race while computing rcv_wnd

HighCVSS 8.2 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 32/100)

  • 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: 0.27% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: Linux Linux 301a33fd590c408a05c5df800e0cc1e6a8a2f8f8, 3b8cbba7c0ed31189c89f90be247b8973ffa79ef, 68364963e5baf03f16b4420292291f75c8f66497.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 301a33fd590c408a05c5df800e0cc1e6a8a2f8f8, 3b8cbba7c0ed31189c89f90be247b8973ffa79ef, 68364963e5baf03f16b4420292291f75c8f66497 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: mptcp: close TOCTOU race while computing rcv_wnd The MPTCP output path access locklessly the MPTCP-level ack_seq in multiple times, using possibly different values for the data_ack in the DSS option and to compute the announced rcv wnd for the same packet. Refactor the cote to avoid inconsistencies which may confuse the peer. Also ensure that the MPTCP level rcv wnd is updated only when the egress packet actually contains a DSS ack.

Published
Jul 19, 2026
Updated
Oct 26, 2026
EPSS
0.2% · 20th percentile

Report tools

JSON

Action score

32

Monitor

Low priority for now.

CVSS
32 / 40 · 8.2 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
8.2
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-2026-63867

When you'll hear from us

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  • 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

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

    • 5.11affected
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before 301a33fd590c408a05c5df800e0cc1e6a8a2f8f8affected · git
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before 68364963e5baf03f16b4420292291f75c8f66497affected · git
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before 907ac6b1658e0277f979fcdfae2a753b495c1510affected · git
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before c4f4cf60797974873dbc8e100144682a6f2f861faffected · git
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before 3b8cbba7c0ed31189c89f90be247b8973ffa79efaffected · git
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before 8f4f0a157e8436a05bf8c3670b24dbc258911c43affected · git
    • fa3fe2b150316b294f2c662653501273ff25bba8 and later · before 8ab24fdebc369c0dfb90f82c1650b1e66662bb45affected · git
    • before 5.11not affected · semver
    • 5.15.210 and later · up to and including 5.15.*not affected · semver
Affected versions · NVD (7)

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

  • linux linux kernel5.11 and later · before 5.15.210
  • linux linux kernel5.16 and later · before 6.1.176
  • linux linux kernel6.2 and later · before 6.6.143
  • linux linux kernel6.7 and later · before 6.12.94
  • linux linux kernel6.13 and later · before 6.18.36
  • linux linux kernel6.19 and later · before 7.0.13
  • linux linux kernel7.1

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 6.12.94-16.12.94-1
Debian:14linuxbefore 7.0.13-17.0.13-1

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-2026-63865Jul 19, 2026 · bpf: Drop task_to_inode and inet_conn_established from lsm sleepable hooks
    35Monitor
  • ← EarlierCVE-2026-63866Jul 19, 2026 · wifi: mt76: mt7996: Clear wcid pointer in mt7996_mac_sta_deinit_link()
    35Monitor
  • Later →CVE-2026-63868Jul 19, 2026 · net: garp: fix unsigned integer underflow in garp_pdu_parse_attr
    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 Linux301a33fd590c408a05c5df800e0cc1e6a8a2f8f8Vendor (CNA)
Linux Linux3b8cbba7c0ed31189c89f90be247b8973ffa79efVendor (CNA)
Linux Linux68364963e5baf03f16b4420292291f75c8f66497Vendor (CNA)
Linux Linux8ab24fdebc369c0dfb90f82c1650b1e66662bb45Vendor (CNA)
Linux Linux8f4f0a157e8436a05bf8c3670b24dbc258911c43Vendor (CNA)
Linux Linux907ac6b1658e0277f979fcdfae2a753b495c1510Vendor (CNA)
Linux Linuxc4f4cf60797974873dbc8e100144682a6f2f861fVendor (CNA)
debian:linux6.1.176-1 · Debian:12Package 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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Variant candidates

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

  • CVE-2025-38352362 days apartposix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()KEV
    61This week
  • CVE-2026-640910 days apartbatman-adv: tt: fix TOCTOU race for reported vlans
    39Monitor
  • CVE-2026-640340 days apartnet: mana: Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer
    37Monitor
  • CVE-2026-639370 days apartKVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer
    35Monitor
  • CVE-2026-641120 days apartrbd: eliminate a race in lock_dwork draining on unmap
    31Monitor
  • CVE-2026-5314524 days apartdrm/gem: Try to fix change_handle ioctl, attempt 4
    31Monitor

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Not on record for this CVE: patch commit or PR link · researcher credit · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

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

Weakness class (CWE)

CWE-367 · Time-of-check Time-of-use (TOCTOU) Race Condition

CVSS vector

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

—

References

Show all references (6 more)

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

All records