---
id: CVE-2026-63828
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  apparmor: mediate the implicit connect of TCP fast open sendmsg

  sendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and
  write(2): it opens the connecti…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  apparmor: mediate the implicit connect of TCP fast open sendmsg

  sendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and
  write(2): it opens the connecti…
severity: high
cvss: 8.4
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N'
published: '2026-07-19'
updated: '2026-08-17'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63828'
references:
  - url: 'https://git.kernel.org/stable/c/07b71c342382b854ab8030b244aeab6a7228ad7d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/20383429b56974507c465d016e5238b189f7a246'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/45ebb934ea50b436ce49b2f159f090dab0d7fa28'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4a69b83045d3195d5b9a9b053ad840ddb2998b4e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4d587cd8a72155089a627130bbd4716ec0856e21'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7f57428ce00891d26b0f087ef754a4d820ec83aa'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a16714e7cf2baa98ba2efddd5d6cbac641f4e76b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/faea60deaa05c76f0772650f42eafde12bd39d93'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - exploit-available
epss: 0.0017
epssPercentile: 0.05591
ingestedAt: '2026-08-17T05:47:50.025Z'
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/4n4s4zi/tfo-connect-bypass'
  checkedAt: '2026-09-26T09:05:55.115Z'
exploitAvailable: true
---

## Overview

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

apparmor: mediate the implicit connect of TCP fast open sendmsg

sendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and
write(2): it opens the connection in the SYN. apparmor_socket_sendmsg()
only checks AA_MAY_SEND, so a profile that grants send but denies connect
lets a confined task open an outbound TCP/MPTCP connection that connect(2)
would have refused, bypassing connect mediation.

Mediate the implicit connect when MSG_FASTOPEN is set and a destination
is supplied. Add it to apparmor_socket_sendmsg() (not the shared
aa_sock_msg_perm() helper, which recvmsg also uses) and call aa_sk_perm()
directly, mirroring the selinux and tomoyo fixes. sk_is_tcp() does not
cover MPTCP fast open, so the SOCK_STREAM/IPPROTO_MPTCP arm is explicit.

## Remediation

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