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Date: Wed, 10 May 2023 18:55:46 +0200
From: Solar Designer <>
To: Turritopsis Dohrnii Teo En Ming <>
	Piotr Krysiuk <>
Subject: Re: New Linux kernel NetFilter flaw gives attackers root privileges


On Wed, May 10, 2023 at 11:52:58PM +0800, Turritopsis Dohrnii Teo En Ming wrote:
> I have just come across this article. Thought of sharing it.
> Article: New Linux kernel NetFilter flaw gives attackers root privileges
> Link:

We don't normally want in here links to news articles on something that
was already brought up in here in more detail.  However, as a moderator,
I reluctantly approved this posting so that we can use the resulting
thread to discuss whether this issue got blown out of proportion and if
so what we can do to avoid that going forward.  Here's the original
posting this refers to:

Another Linux kernel issue, in io_uring subsystem, was also disclosed in
here on the same day, but I think didn't gain such tech media attention:

Is the netfilter issue really worse than the io_uring issue?  I doubt
it.  So _maybe_ it was something in the wording that tripped someone
writing for one of those tech news websites, then others picked it up?

Piotr's posting about the netfilter issue mentions intent to disclose an
exploit later (like it should have, thank you Piotr!)

Tobias' posting directly links to an exploit (which is also fine).

Is intent to disclose an exploit later more newsworthy than having done
so right away?  I doubt it.

So maybe it's just random, and there's nothing to see here, after all.

Now as to the actual issue and its description, I think we should
clarify what exactly is meant by "unprivileged local users."  Piotr, I
guess you actually meant not literally unprivileged, but users with
CAP_NET_ADMIN, which can be had via unprivileged user/net namespaces if
enabled in the distro / on the system, or when already in a container
with such capability granted to container root.  Correct?  I think going
forward we should always make this clear right away.  Here's a former
netfilter core team leader also bringing this up:

LaForge - @LaF0rge:
> Really curious to see how CVS-223-32233 for #linux #netfilter nf_tables
> can be exploted fom
> "unprivileged local users".  AFAICT, nf_tables_api  goes through
> nfnetlink, and nfnetlink_rcv() checks for CAP_NET_ADMIN way  before the
> code in nf_tables_api.

and a reply:

Alex Plaskett @alexjplaskett:
> Didn't look in depth at this one but you can trigger nf_tables_api
> operations from a user / network namespace and distros such as Ubuntu
> have unpriv user namespaces enabled.

As expected.  Now, from a typical distro user's standpoint,
"unprivileged local users" may be just right.  However, not all distros
have unprivileged user namespaces enabled by default.


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