Re: ISA Server detected a spoof attack

  • From: "Jim Harrison" <jim@xxxxxxxxxxxx>
  • To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
  • Date: Wed, 14 Jan 2004 13:20:30 -0800

Aha!
He said VLAN!
neener-neener-boo-boo...
=^p

Check your switch; looks like your VLAN is busted.

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message ----- 
From: "Eric Poole" <EPoole@xxxxxxxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, January 14, 2004 13:18
Subject: [isalist] Re: ISA Server detected a spoof attack


http://www.ISAserver.org

OK, now I'm getting confused. :)  Cisco is on the same subnet as the internal 
NIC.  External is supposed to be on it's own vlan.

_______________________________________________
Eric Poole
IS Security Analyst
Community Medical Centers
1140 "T" Street, Fresno, California 93721
559-459-6784 (phone) 559-459-2045 (fax)


-----Original Message-----
From: Dan Bartley [mailto:bartleyd@xxxxxxxxxxxxxxxxxxx] 
Sent: Wednesday, January 14, 2004 1:02 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: ISA Server detected a spoof attack

http://www.ISAserver.org

Yep, you're right. I transposed DNS and Default Gateway when I looked at
them.

Best Regards, 

Dan Bartley

-----Original Message-----
From: Jim Harrison [mailto:jim@xxxxxxxxxxxx] 
Sent: Wednesday, January 14, 2004 15:45
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: ISA Server detected a spoof attack

http://www.ISAserver.org

Actually, that's not the case.

internal     = 172.16.10/24
external    = 172.16.2/24
Cisco       = 172.16.10.168

The log data states that the packet was sent from the Cisco to the ISA
"external" NIC.
172.16.10.168, 172.16.2.9, ICMP, 8, 0, -, BLOCKED,172.16.2.9

According to the IP assignments, the Cisco is "internal", but the packet
was received on the ISA external interface according to the
log entry.  That's why I suggested a misplaced cable or broken VLAN.

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message ----- 
From: "Dan Bartley" <bartleyd@xxxxxxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, January 14, 2004 12:20
Subject: [isalist] Re: ISA Server detected a spoof attack


http://www.ISAserver.org

Not necessarily. Is the Cisco on the same private subnet as the external
NIC of ISA, and is that different from the private subnet being used by
the internal ISA NIC?

Could be set up as a second level defense behind the Cisco and a
firewall. That would allow for a private IP on the external NIC.

What I see below from his ipconfig/all seems to indicate that is the
case.

Best Regards,

Dan Bartley

-----Original Message-----
From: Jim Harrison [mailto:jim@xxxxxxxxxxxx]
Sent: Wednesday, January 14, 2004 15:16
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: ISA Server detected a spoof attack

http://www.ISAserver.org

The fact that ISA is receiving traffic from an internal IP on the
external NIC seems to hint that you have a cable misplaced or a
VLAN is broken.

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message ----- 
From: "Eric Poole" <EPoole@xxxxxxxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, January 14, 2004 11:53
Subject: [isalist] Re: ISA Server detected a spoof attack


http://www.ISAserver.org

ISA's internal is on the .10 subnet just like the cisco box.  ISA's
external is on the .2 subnet.  The external (2.9) is on a
separate vlan, so it's virtually external.
"Ethernet adapter Intranet:
  Connection-specific DNS Suffix  . :
        Description . . . . . . . . . . . : HPNC7781 Gigabit Server
Adapter
        Physical Address. . . . . . . . . : 00-0B-CD-82-2A-45
        DHCP Enabled. . . . . . . . . . . : No
        IP Address. . . . . . . . . . . . : 172.16.10.110
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . :
        DNS Servers . . . . . . . . . . . : 172.16.10.41
                                            172.18.52.41
        Primary WINS Server . . . . . . . : 172.16.10.41
        Secondary WINS Server . . . . . . : 172.16.11.41

Ethernet adapter Extranet:
  Connection-specific DNS Suffix  . :
        Description . . . . . . . . . . . : HPNC7781 Gigabit Server
Adapter2
        Physical Address. . . . . . . . . : 00-0B-CD-82-2A-6A
        DHCP Enabled. . . . . . . . . . . : No
        IP Address. . . . . . . . . . . . : 172.16.2.9
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 172.16.2.20
        DNS Servers . . . . . . . . . . . :
        NetBIOS over Tcpip. . . . . . . . : Disabled"


_______________________________________________
Eric Poole
IS Security Analyst
Community Medical Centers
1140 "T" Street, Fresno, California 93721
559-459-6784 (phone) 559-459-2045 (fax)


-----Original Message-----
From: Jim Harrison [mailto:jim@xxxxxxxxxxxx]
Sent: Wednesday, January 14, 2004 11:33 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: ISA Server detected a spoof attack

http://www.ISAserver.org

What does the ISA "ipconfig/all" produce?
It sounds like ISA doesn't really agree with you about what's internal.


 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message ----- 
From: "Eric Poole" <EPoole@xxxxxxxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, January 14, 2004 10:32
Subject: [isalist] ISA Server detected a spoof attack


http://www.ISAserver.org

I'm getting these about every half hour from our internal Cisco Works
box (172.16.10.168).  The 2.9 address is the ISA external NIC
that is routed through our PIX.  Any ideas?

"ISA Server detected a spoof attack from Internet Protocol (IP) address
172.16.10.168. A spoof attack occurs when an IP address that
is not reachable via the interface on which the packet was received. If
logging for dropped packets is set, you can view details in
the packet filter log."

Here's a sample from the packet filter log.

"1/13/2004, 20:43:17, 172.16.10.168, 172.16.2.9, ICMP, 8, 0, -, BLOCKED,
172.16.2.9, 45 00 00 3c 20 74 00 00 7f 01 b6 7b ac 10 0a a8
ac 10 02 09, 08 00 a1 b6 04 00 77 6e ad ad ad ad ad ad ad ad ad ..."

_______________________________________________
Eric Poole
IS Security Analyst
Community Medical Centers
1140 "T" Street, Fresno, California 93721
559-459-6784 (phone) 559-459-2045 (fax)

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