CVE-2026-63828

Description

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.

References

• 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