Hi FreeBSD Gurus,
i want to use PF to Preventing SMTP Brute Force Attacks. i need some help
to understand correct syntax.
URL Explaining this: http://www.openbsd.org/faq/pf/filter.html#stateopts
i expect the following behavior from the PF rule below:
Limit the absolute maximum number of states that this rule can create to 200
Enable source tracking; limit state creation based on states created by
this rule only
Limit the maximum number of nodes that can simultaneously create state to 100
Limit the maximum number of simultaneous states per source IP to 3
Solution:
int0="em0"
trusted_tcp_ports="{22,25,443,465}"
pass in on $int0 proto tcp from any to any port $trusted_tcp_ports keep
state max 200, source-track rule, max-src-nodes 100, max-src-states 3
please help ..
Thanks / Regards
On 15/06/2012 17:17, Shiv. Nath wrote:> Hi FreeBSD Gurus, > > > i want to use PF to Preventing SMTP Brute Force Attacks. i need some help > to understand correct syntax. > > URL Explaining this: http://www.openbsd.org/faq/pf/filter.html#stateopts > > > i expect the following behavior from the PF rule below: > > Limit the absolute maximum number of states that this rule can create to 200 > > Enable source tracking; limit state creation based on states created by > this rule only > > Limit the maximum number of nodes that can simultaneously create state to 100 > > Limit the maximum number of simultaneous states per source IP to 3 > > Solution: > int0="em0" > trusted_tcp_ports="{22,25,443,465}" > > pass in on $int0 proto tcp from any to any port $trusted_tcp_ports keep > state max 200, source-track rule, max-src-nodes 100, max-src-states 3Limiting yourself to 200 states won't protect you very much -- you tend to get a whole series of attacks from the same IP, and that just uses one state at a time. Instead, look at the frequency with which an attacker tries to connect to you. Something like this: table <bruteforce> persist [...] block in log quick from <bruteforce> [...] pass in on $ext_if proto tcp \ from any to $ext_if port $trusted_tcp_ports \ flags S/SA keep state \ (max-src-conn-rate 3/300, overload <bruteforce> flush global) Plus you'll need a cron job like this to clean up the bruteforce table, otherwise it will just grow larger and larger: */12 * * * * /sbin/pfctl -t ssh-bruteforce -T expire 604800 >/dev/null 2>&1 The end result of this is that if one IP tries to connect to you more than 3 times in 5 minutes, they will get blacklisted. I normally use this just for ssh, so you might want to adjust the parameters appropriately. You should also implement a whitelist for IP ranges you control or use frequently and that will never be used for bruteforce attacks: it is quite easy to block yourself out with these sort of rules. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate JID: matthew@infracaninophile.co.uk Kent, CT11 9PW -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 267 bytes Desc: OpenPGP digital signature Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20120615/8068b1c0/signature.pgp
On Fri, Jun 15, 2012 at 04:17:06PM -0000, Shiv. Nath wrote:> Hi FreeBSD Gurus, > > > i want to use PF to Preventing SMTP Brute Force Attacks. i need some help > to understand correct syntax. > > URL Explaining this: http://www.openbsd.org/faq/pf/filter.html#stateopts > > > i expect the following behavior from the PF rule below: > > Limit the absolute maximum number of states that this rule can create to 200 > > Enable source tracking; limit state creation based on states created by > this rule only > > Limit the maximum number of nodes that can simultaneously create state to 100 > > Limit the maximum number of simultaneous states per source IP to 3 > > Solution: > int0="em0" > trusted_tcp_ports="{22,25,443,465}" >pass in on $int0 proto tcp from any to any port $trusted_tcp_ports keep state (max 200, source-track rule, max-src-nodes 100, max-src-states 3 ) I don't know if max will work here but this is what I use for a sshd rule. pass in log quick proto tcp from any port >1023 to any port 22 flags S/SA keep state (max-src-conn 5, max-src-conn-rate 5/15 overload <sshmart> flush global) You should be using the syntax from pf41 through pf45. The URL you referenced has a syntax that changed in pf46, pf47 onward... -- - (2^(N-1))
> On Jun 15, 2012, at 12:55 PM, Shiv. Nath wrote: > >> # START >> table bruteforce persist >> block in log quick from bruteforce >> >> pass in on $ext_if proto tcp \ >> from any to $ext_if port $trusted_tcp_ports \ >> flags S/SA keep state \ >> (max-src-conn-rate 3/300, overload bruteforce flush global) >> >> # END >> >> AND CRON: >> */12 * * * * /sbin/pfctl -t ssh-bruteforce -T expire 604800 >/dev/null >> 2>&1 >> >> What is the function "expire 604800" are they entries in the table? >> should it be -t bruteforce or -t ssh-bruteforce > > > It refers to entries in the table specified by the "-t" option and > instructs pf to expire (remove from the table) all entries older than the > specified time (in seconds). Basically, the value 604800 will expire > entries older than 1 week. > > For the above pf rules, the cron entry should be "-t bruteforce" (although > in the pf rules you should be using "<bruteforce>"). > > Cheers, > > Paul. > > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" >Dear Metthew & Paul, Thank you very much for your time, efforts and energy to help me configuring PF. Metthew also advised to create white, so that i do not lock myself. i have have to yet look at it. i will get in touch if i require more help. Thanks Regards