CVE Catalog

CVE-2026-63828

HighCVSS 8.4
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.13%

3th percentile - higher than 3% of all known CVEs

Summary

Vulnerability in the Linux kernel AppArmor module allows bypassing connect mediation by using MSG_FASTOPEN flag in sendmsg(). A profile allowing send but blocking connect can be bypassed.

Risk Assessment

A confined process can establish TCP/MPTCP connections that would normally be blocked, potentially leading to unauthorized access to external networks.

Recommendation

Apply the Linux kernel patch that adds implicit connect mediation in apparmor_socket_sendmsg() for MSG_FASTOPEN.

Other vulnerabilities in Linux kernel

See all
Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS