this post was submitted on 29 Oct 2026
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[–] rimu@piefed.social 38 points 2 days ago* (last edited 2 days ago) (2 children)

You can disable multipath TCP by issuing this command

sudo sysctl -w net.mptcp.enabled=0

persist across reboots with

echo "net.mptcp.enabled=0" | sudo tee /etc/sysctl.d/99-mptcp.conf


If your kernel is older than 5.6 then there is no multipath TCP to disable. e.g. Ubuntu 20.04 should be fine.

[–] walderan@sh.itjust.works 2 points 1 day ago* (last edited 1 day ago)

Tacking this on here to increase visibility.
You can see who is already listening to multipath TCP by running:

ss -Mln

running the sysctl command will prevent future ports being opened, but it will not close existing ones, you need to manually restart the services/containers.
Go applications enable the functionality in their ports by default.
My understanding is that a proper fix will come from a kernel update, since this affects plain TCP, but MPTCP has a known attack path.

[–] ImgurRefugee114@reddthat.com 34 points 2 days ago

Note: It's unclear whether this is an adequate mitigation.