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Patrick Milvich

2007-Dec-11 22:58 UTC

[Dovecot] Fishing attempt locking up dovecot

I've mentioned this before but only heard from one other person who  
has experienced this, but it's becoming a pretty serious issue.

The situation:
A spammer sets a bot on a fishing attempt to gain email addresses,  
causing numerous login processes to spawn and suck up all available  
resources.

The problem:
Obviously this can act like a dos attack, but the real issue is after  
the spammer stops (by virtue of being added to our firewall blacklist,  
being caught and shut down by their isp, or otherwise), dovecot  
doesn't seem to relinquish the resources, causing "too many files  
open" errors for normal usage.

The master process usually hangs around 40-50 files open at any given  
time, with about 10,000 logins a day (I use: lsof -p `cat /var/run/ 
dovecot/master.pid ` | wc -l), after the attempt is over I always see  
the files open shoot up to near 3,000 without it able to go down until  
a dovecot restart.

This usually happens about once a month, though we can get unlucky and  
have it happen a few days apart. I have some log excerpts below.

Wondering if this is happening through my own fault or at least within  
my ability to alleviate the issue. Is there a way to limit the number  
of connections from an ip address? Has anyone used login_executable to  
first hit their own solution to keep track of, and implement  
connection restrictions similar to what I'm aiming for?

Thanks for any insight
Patrick

dovecot -n
# 1.0.8: /usr/local/mail/dovecot/etc/dovecot.conf
base_dir: /var/run/dovecot/
log_path: /var/log/dovecot
protocols: imap imaps pop3 pop3s
ssl_cert_file: /usr/local/mail/ssl/certs/dovecot.pem
ssl_key_file: /usr/local/mail/ssl/private/dovecot.pem
ssl_cipher_list: ALL:!LOW
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/local/mail/dovecot/libexec/dovecot/ 
imap-login
login_executable(imap): /usr/local/mail/dovecot/libexec/dovecot/imap- 
login
login_executable(pop3): /usr/local/mail/dovecot/libexec/dovecot/pop3- 
login
first_valid_uid: 500
mail_location: maildir:/Volumes/data/mail/%Ld/%Ln
mail_executable(default): /usr/local/mail/dovecot/libexec/dovecot/imap- 
before
mail_executable(imap): /usr/local/mail/dovecot/libexec/dovecot/imap- 
before
mail_executable(pop3): /usr/local/mail/dovecot/libexec/dovecot/pop3- 
before
mail_plugin_dir(default): /usr/local/mail/dovecot/lib/dovecot/imap
mail_plugin_dir(imap): /usr/local/mail/dovecot/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/local/mail/dovecot/lib/dovecot/pop3
pop3_uidl_format(default):
pop3_uidl_format(imap):
pop3_uidl_format(pop3): %08Xu%08Xv
auth default:
   mechanisms: plain digest-md5 login
   passdb:
     driver: sql
     args: /usr/local/mail/dovecot/etc/dovecot-sql.conf
   userdb:
     driver: static
     args: uid=exim gid=exim
plugin:
   quota: maildir


 From the logs, first entries showing the problem:
dovecot: Dec 10 16:17:02 Info: pop3-login: Disconnected:  
rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:02 Info: pop3-login: Disconnected:  
rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:03 Info: pop3-login: Disconnected:  
rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:03 Info: pop3-login: Disconnected:  
rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:03 Info: pop3-login: Disconnected:  
rip=207.245.39.90, lip=<lip>

A little later on:
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login:  
user=<pwitest>, method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login:  
user=<tsinternetuser>, method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login: user=<bill>,  
method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login: user=<web>,  
method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login:  
user=<barbara>, method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login: user=<www>,  
method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login: user=<user>,  
method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login:  
user=<nathan>, method=PLAIN, rip=207.245.39.90, lip=<lip>
dovecot: Dec 10 16:17:12 Info: pop3-login: Aborted login:  
user=<webmaster>, method=PLAIN, rip=207.245.39.90, lip=<lip>

etc. etc.

Asheesh Laroia

2007-Dec-11 23:08 UTC

head link

[Dovecot] Fishing attempt locking up dovecot

On Tue, 11 Dec 2007, Patrick Milvich wrote:
> I've mentioned this before but only heard from one other person who has
> experienced this, but it's becoming a pretty serious issue.
>
> The situation:
> A spammer sets a bot on a fishing attempt to gain email addresses, causing 
> numerous login processes to spawn and suck up all available resources.
Sounds like you could avoid this problem if you configured fail2ban to 
block the spammer trying all these logins.

However, the underlying problem with Dovecot would remain, and so it is 
worth fixing that too!

-- Asheesh.

--
The speed of anything depends on the flow of everything.

Jerry Yeager

2007-Dec-12 03:02 UTC

head link

[Dovecot] Fishing attempt locking up dovecot

On Dec 11, 2007, at 5:58 PM, dovecot-request at dovecot.org wrote:
>
>
> Message: 10
> Date: Tue, 11 Dec 2007 15:58:16 -0700
> From: Patrick Milvich <patrick at milvich.com>
> Subject: [Dovecot] Fishing attempt locking up dovecot
> To: dovecot at dovecot.org
> Message-ID: <8C5CE5FE-BD2F-40C4-8A36-A4CD8BD533DB at milvich.com>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
> I've mentioned this before but only heard from one other person who
> has experienced this, but it's becoming a pretty serious issue.
>
> The situation:
> A spammer sets a bot on a fishing attempt to gain email addresses,
> causing numerous login processes to spawn and suck up all available
> resources.
>
> The problem:
> Obviously this can act like a dos attack, but the real issue is after
> the spammer stops (by virtue of being added to our firewall blacklist,
> being caught and shut down by their isp, or otherwise), dovecot
> doesn't seem to relinquish the resources, causing "too many files
> open" errors for normal usage.
>
>
stuff cut out
>
> End of dovecot Digest, Vol 56, Issue 33
> ***************************************

Will the following be of any help to you? (it is a patch for Postfix  
2.4.nn) It would seem that the type of fishing expedition you mention  
would fall into the bit described below (lots of errors). While it  
will not directly solve the "out of resources" Dovecot problem, it may
limit the up-front damage, followed with a CRON script running every  
twenty minutes or so that scans the last line of the mail log for the  
'too many files open' error and upon finding it runs a version of the  
killall imap-login processes.


ftp://postfix.mirrors.pair.com/index.html


Postfix 2.4 patch (PGP signature ) to add stress-adaptive behavior to  
the SMTP server. When some mail flood keeps all server ports busy,  
this feature can be used to quickly drop connections from clients that  
make errors, and to reduce the time that Postfix waits for a client  
command. This may delay some legitimate deliveries, but it will allow  
you to still keep some mail flowing. After the mail flood ends,  
Postfix reverts to its normal behavior.
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Timo Sirainen

2007-Dec-29 05:38 UTC

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[Dovecot] Fishing attempt locking up dovecot

On Tue, 2007-12-11 at 15:58 -0700, Patrick Milvich
wrote:> Obviously this can act like a dos attack, but the real issue is after  
> the spammer stops (by virtue of being added to our firewall blacklist,  
> being caught and shut down by their isp, or otherwise), dovecot  
> doesn't seem to relinquish the resources, causing "too many files
> open" errors for normal usage.
I guess there could be problems after you get "too many open files",
but
you can configure Dovecot so that it never happens. v1.1 warns about
this at startup.

Basically you just need to make sure that when starting dovecot,
ulimit -n is a bit larger than max_mail_processes +
login_max_processes_count + auth_worker_max_count (if you're using
MySQL).

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