A flaw allows a confined task that has permission to send data to open a TCP or MPTCP connection via the sendmsg()/sendto() system call using the MSG_FASTOPEN flag, without being subjected to the AppArmor connect mediation that would normally deny the operation. The bug arises because the AppArmor socket logic checked only the SEND permission, not the CONNECT permission, for this particular operation. An attacker controlling a confined process can thus establish an outbound connection bypassing AppArmor profiles designed to block such traffic, potentially exfiltrating data or communicating with an attacker‑controlled host.

All Linux kernel installations before the patch that adds the implicit connect permission check for sendmsg() with MSG_FASTOPEN are affected. The vulnerability applies to the generic Linux kernel platform, so any unpatched kernel version is vulnerable.

The exposure carries a CVSS score of 8.4, indicating high severity. The EPSS score is listed as < 1%, suggesting that exploitation attempts are expected to be very uncommon at this time. The vulnerability is not currently cataloged in the CISA KEV list. Attackers would need to execute or influence a confined task that can invoke sendmsg() with MSG_FASTOPEN; once this is achieved, they can open outbound connections that are otherwise prohibited by AppArmor, enabling data exfiltration or remote command reachability. Given that the flaw requires specific system call usage and a compromised confined process, the likelihood of exploitation is low but the potential impact remains significant for systems relying on AppArmor to enforce strict network restrictions.