Vulnerability Report

CVE-2026-63828

Title: Apparmor: mediate TCP fast open sendmsg connect

Other

Proof Of Concept

PoC Available for CVE-2026-63828

CWE Category NVD-CWE-noinfo

Published Date Jul 19, 2026

Modified Date Aug 17, 2026

Exploit Status Available

Score 8.4 CVSS v

Exploit Probability (EPSS)

0.17%

Vulnerability Summary

CVE-2026-63828: 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.

Impacted Vendors

Analysis in Progress...

Reference Links

https://git.kernel.org/stable/c/07b71c342382b854ab8030b244aeab6a7228ad7d https://git.kernel.org/stable/c/45ebb934ea50b436ce49b2f159f090dab0d7fa28 https://git.kernel.org/stable/c/4a69b83045d3195d5b9a9b053ad840ddb2998b4e https://git.kernel.org/stable/c/4d587cd8a72155089a627130bbd4716ec0856e21 https://git.kernel.org/stable/c/7f57428ce00891d26b0f087ef754a4d820ec83aa https://git.kernel.org/stable/c/faea60deaa05c76f0772650f42eafde12bd39d93

CVSS v3.1

Source Entity 416baaa9-dc9f-4396-8d5f-8c081fb06d67

Severity HIGH

8.4

Attack Vector

LOCAL

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

CHANGED

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

Associated Attack Patterns (CAPEC)

Total: Patterns