CVE-2025-68291

A divide-by-zero vulnerability was found in the MPTCP implementation in the Linux kernel. When mptcp_do_fastclose() calls tcp_send_active_reset(), the rcv_mss field is uninitialized (zero), causing a division by zero in __tcp_select_window(). This results in a kernel crash.

This can be triggered through MPTCP socket operations during fast close scenarios. The impact is denial of service via kernel panic.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Disable Multipath TCP (MPTCP) if it is not required in your environment.

To disable MPTCP immediately:

sysctl -w net.mptcp.enabled=0

To make the configuration persistent across system reboots, execute:

echo 'net.mptcp.enabled = 0' > /etc/sysctl.d/99-disable-mptcp.conf

sysctl --system

Caveats: Disabling MPTCP prevents applications from creating MPTCP sockets, forcing connections to fall back to standard TCP or causing socket creation to fail if applications strictly require MPTCP. Applying sysctl takes effect immediately for newly created sockets without requiring a system restart, but any pre-existing MPTCP connections must be terminated to fully eliminate exposure.