Author: Jasen Betts Date: To: exim-users Subject: Re: [exim] refused: too many connections
On 2013-12-19, Gary Stainburn <gary.stainburn@???> wrote: > On a number of occassions I've had my server DOS'd because of a number of
> incoming connections hanging and then getting hundreds of the following entry
> in my logs (different IP's)
>
> /var/log/exim/main.log-20131215:2013-12-13 19:08:15 Connection from
> [85.137.122.107] refused: too many connections
>
> If I look at exiwhat I see things like
>
> 29719 handling incoming connection from mail.orovia.com [109.108.128.13]
>
> hanging around for long periods. In the case of the above IP address, the
> connections did not close, then multiple connections used up multiple
> connections hence the DOS.
>
> I now block that IP on my server using the acl_smtp_connect ACL. which has
> stopped the DOS attack, but while I've been monitoring the server I have seen
> a number of IP's that sit there for much longer than they should. I have
> reduced smtp_receive_timeout to 4m which is probably how long these
> connections are staying open.
>
> My questions are:
>
> 1) is there a way to catch these time-outs so that the offending IP address
> can be recorded?
log something in ACL_NOTQUIT
> 2) Is there a way to time how long a message takes? If possible, timing
> seperate stages of the delivery?
log more stuff, also the exim-id is based on the timestamp when they said 'data'
> I currently have a manually maintained file /etc/exim/ip_blacklist.lst which
> gets checked as part of the acl_smtp_connect ACL.
>
> I am looking to have exim maintain a SQL table adding enties for offending IPs
I use that approach, it seems to work ok.
fail2ban, an exim's own ratelimit may be other options
