Cisco ASA 5510 DMZ attack issues

Posted on 2010-09-21
Last Modified: 2013-11-16
We are having problems with attacks on our web servers.
We have an ASA 5510 and it reports 120+ scanning attacks and 60+ SYN attacks.
When these are higher than 5 the web servers go extremely slow and do not respons.
This is happening for longer periods of time now.
Basic threat detection is enabled, scanning threat detection is enabled and Shun Hosts.

Can anyone help?

Question by:CTEC
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LVL 17

Accepted Solution

Kvistofta earned 500 total points
ID: 33726203
Do you have any max conns or embrionics-limit defined in the static for your web server?

By setting a limit for this you make your firewall protect your web server from syn attacs.


Author Comment

ID: 33726231
i have embrionics-limit set to 25 on the web servers

Author Comment

ID: 33726258
static (DMZ,outside) ***.***.***.*** ***.***.***.*** netmask dns tcp 0 25
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LVL 17

Expert Comment

ID: 33726544
And you are still getting 60+ half-open connections to the web-server???


Author Comment

ID: 33726980
yes, currently ASDM reports under firewall dashboard:

Scanning attacks: 122
SYN attacks: 85
LVL 17

Expert Comment

ID: 33727034
Ok. But do you have any performance issues on your web server? What you see just indicates that the firewall does what it is built to do. If you do not want to see the firewall identifying and/or blocking attacks you need to protect it with another firewall infront of it. .-)


Author Comment

ID: 33727150
when the firewall reports high scanning attacks and SYN attacks the webservers will not respond to http requests, if i stop inbound traffic the webservers work normally

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