[no subject]

[Duane Dunston <ddunston () CAPEFEAR CC NC US>]

I was curious to know if someone could reproduce this problem as Borderware hasn't gotten back to me since the end of 
November 2000 regarding this issue.  I pinged the broadcast again, doing regular test on January 22nd 2001, and the 
same thing occured.

####

The Problem

#### 

OS/application:

Borderware firewall server v. 6.1.2

Unsure if it affects lower versions of the Borderware Firewall Server.

Exploit:

Sending a ping to the broadcast on the network causes Borderware's ping 

server to continously send echo request to the entire network. It is 

possible that a Denial-of-Service attack (smurf attack) can be executed on 

the network using freely available exloit code. This can occur externally 

if broadcast packets aren't dropped at the router or on the local network 

if other machines aren't configured to deny directed broadcasts.

This will not affect networks behind the Borderware Firewall but it will 

affect machines on the same network as the Borderware's public interface.

Reproducing the exploit:

ping xxx.xxx.xxx.255 or ping xxx.xxx.xxx.0/24 (the -f switch will perform 

a ping flood, see the ping man page for more info) 

There are freely available smurf attack exploits available on the internet 

as well (run a search for "smurf attack" at packetstorm.securify.com)

Fixes:

Borderware doesn't give users access to the console to restart the ping 

server so you have to call them to restart it remotely.

For machines on the network that are responding to the broadcasts running 

Linux, you can add "1" to the /proc/sys/net/ipv4/icmp_echo_ignore_broadcast

s file:

# echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

or add it to your /etc/sysctl.conf file (recommended):

net.ipv4.icmp_echo_ignore_broadcasts = 1

then run:

# sysctl -w (to update the change)

On a cisco router this line will prevent replies to a directed broadcast:

deny ip any 0.0.0.255 255.255.255.0 (Taken from http://www.sans.org/infosec

FAQ/firewall/perimeter_filter.htm)

Related info on Smurf Attacks:

http://www.cert.org/advisories/CA-1998-01.html

--

metta,

Duane Dunston
Unix Technical Specialist
Cape Fear Community College
(910) 251-5839
 
 
"When three men are walking together, there
is one who can be my teacher. I pick out
people's good and follow it. When I see their
bad points, I correct them in myself."
 
--Confucius