---
id: CVE-2026-63913
title: >-
  netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without
  direction check
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without
  direction check


  An unintended behavior in the TCP conntrack state machine allows a

  connection …
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    2006979a15af5404bf932a325357683c0bac1656
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    6476c17d536dbd321c073242e762ddb2713a1238
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    f5547bebc416d56f56fb5b86dc20aabfa42165a0
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    f206def4e86d810f927ba1d8e322ea72b29bce58
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    b98ab51c45c5608a1c19ce7fd17a3032469bb83f
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    d67c6adee8d1b65330d0174c4c367faba14e80a8
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a
  - Linux 2.6.15
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-16T15:33:11.442709Z'
published: '2026-07-19'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:42:10.956Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-63913'
references:
  - url: 'https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656'
  - url: 'https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238'
  - url: 'https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0'
  - url: 'https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77'
  - url: 'https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58'
  - url: 'https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f'
  - url: 'https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8'
  - url: 'https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a'
tags:
  - cve.org
epss: 0.00971
epssPercentile: 0.61281
ingestedAt: '2026-10-16T17:24:46.776Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check

An unintended behavior in the TCP conntrack state machine allows a
connection to be forced into the CLOSE state using an RST packet with an
invalid sequence number.

Specifically, after a SYN packet is observed, an RST with an invalid SEQ
can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of
whether the RST corresponds to the expected reply direction. The relevant
code path assumes the RST is a response to an outgoing SYN, but does not
validate packet direction or ensure that a matching SYN was actually sent
in the opposite direction.

As a result, a crafted packet sequence consisting of a SYN followed by an
invalid-sequence RST can prematurely terminate an active NAT entry. This
makes connection teardown easier than intended.

So, tighten the state transition logic to ensure that RST-triggered
CLOSE transitions only occur when the RST is a valid response to a
previously observed SYN in the correct direction.

## Affected

- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 2006979a15af5404bf932a325357683c0bac1656`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 6476c17d536dbd321c073242e762ddb2713a1238`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < f5547bebc416d56f56fb5b86dc20aabfa42165a0`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < f206def4e86d810f927ba1d8e322ea72b29bce58`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < b98ab51c45c5608a1c19ce7fd17a3032469bb83f`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < d67c6adee8d1b65330d0174c4c367faba14e80a8`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a`
- `Linux 2.6.15`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.