Re: [exim] Blocking a Class C

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Author: The Doctor
Date:  
To: Odhiambo Washington
CC: Evgeniy Berdnikov, exim-users
Subject: Re: [exim] Blocking a Class C
On Thu, Dec 08, 2022 at 11:44:44PM +0300, Odhiambo Washington via Exim-users wrote:
> On Thu, Dec 8, 2022 at 11:38 PM The Doctor via Exim-users <
> exim-users@???> wrote:
>
> > On Thu, Dec 08, 2022 at 10:47:18PM +0300, Evgeniy Berdnikov via Exim-users
> > wrote:
> > > On Thu, Dec 08, 2022 at 12:22:13PM -0700, The Doctor via Exim-users
> > wrote:
> > > > On Thu, Dec 08, 2022 at 09:24:19PM +0300, Odhiambo Washington via
> > Exim-users wrote:
> > > [...]
> > > > > >>> host in "5.34.207.0/24"? yes (matched "5.34.207.0/24")
> > > > > >>> host in host_reject_connection? yes (matched "+host_rejects")
> > > > > LOG: refused connection from [5.34.207.3] (host_reject_connection)
> > > > > 554 SMTP service not available
> > > > > root@gw:/usr/home/wash #
> > > >
> > > > Still seeing
> > > >
> > > > netstat -a | egrep smtp
> > > > tcp4       0      0 exploreedmonton..smtps 5.34.207.189.26526
> >  SYN_RCVD
> > > > tcp4       0      0 comparealbertapo.smtps 5.34.207.190.30872
> >  FIN_WAIT_2
> > > > tcp4       0      0 204.209.81.148.smtps   5.34.207.114.57546
> >  FIN_WAIT_2

> > >
> > > Rejection with status code 554 requires established TCP connection.
> > > Study mainlog to check whether connections are rejected.
> > >
> > > However, absense of numerous connections in ESTABLISHED state is a hint
> > > that rejection works.
> > >
> > > If you don't want TCP connections, use packet filtering on kernel level
> > > instead of Exim's configuration options.
> >
> > I am surprised that my firewall ACL is not getting this
> > in a switch!
>
>
> I shared config snippets that work.
> If you wanted to deal with this at the firewall level, you did not need
> Exim to do it!
>


As I said, the firewall wer not dropping the packets hence the
need to use exim ACL.

By the way,

This looks like a very interesting attack!

Have a look at https://www.nk.ca/~doctor/5.34.207.txt

but be careful!

This file is 113960735 bytes.

> --
> Best regards,
> Odhiambo WASHINGTON,
> Nairobi,KE
> +254 7 3200 0004/+254 7 2274 3223
> "Oh, the cruft.", egrep -v '^$|^.*#' ??\_(???)_/?? :-)
> --
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