Mod_evasive not blocking a DOS attack using HEAD requests

Question

Using Apache/2.2.15 on RHEL6 with mod_evasive config:

DOSHashTableSize    3097
DOSPageCount        14
DOSPageInterval     2
DOSSiteCount        70
DOSSiteInterval     1
DOSBlockingPeriod   60

Unfortunately it didn't block this attack, which only came from 1 IP:

207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:53 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:53 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:53 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"
207.xxx.xxx.xxx - - [14/Jun/2015:06:06:54 +0400] "HEAD / HTTP/1.1" 200 - "-" "some fake user agent"

Mod_evasive does work, it blocks some IPs in other cases. Does it not work for HEAD requests?

EDIT: My apache is running in prefork mode. From what I've read mod_evasive has issues with it.

score 0 · Answer 1 · answered Jun 16 '15 at 17:37

Modify the variable to something lower, 14 is really high.

DOSPageCount 3

Since the attack is coming from the same place, you can ban the IP address.

sudo iptables -t raw -I PREROUTING -s 207.x.x.x/32 -j DROP

Or you can install mod_security, set it up and add "some fake user agent" to the bad_robots.data file and it will be greeted with a 401 forbidden.

NOTE

DDoS attacks are designed to consume bandwidth as well as resources. You can ban an IP address, lock them out with mod_evasive or reject their requests with 401. NONE OF THESE METHODS WILL NOT STOP A DDoS. DDoS will continue to consume all your bandwidth still keeping your device offline. The best method is to contact your ISP and ask them to blackhole the offending IPs or contact a DDoS mitigation service such as cloudflare. Nothing else you do will stop the DDoS.

If you are under constant DDoS, use a DDoS mitigation service. NONE of the previous methods mentioned will stop a DDoS.

Mod_evasive not blocking a DOS attack using HEAD requests

1 Answers1