You don't see any ports because these are packet fragments (hence the
"offset <number>"). This looks like some sort of malicious traffic
because the offset of each sequential packet is wrong, the next offset
is starting before the last one ended. These overlapping values are an
older type of attack called a Teardrop attack.
-----Original Message-----
From: Mihai Tanasescu [mailto:mihai@duras.ro]
Sent: Thursday, October 13, 2005 1:09 PM
To: incidents@securityfocus.com
Subject: Strange attack question - seems udp
Hello,
I've been getting things like these recently:
21:00:52.941148 IP (tos 0x0, ttl 127, id 28639, offset 11840, flags [+],
length: 1500) 86.104.102.16 > 70.84.247.164: udp
21:00:52.941271 IP (tos 0x0, ttl 127, id 28639, offset 13320, flags [+],
length: 1500) 86.104.102.16 > 70.84.247.164: udp
21:00:52.941394 IP (tos 0x0, ttl 127, id 28639, offset 14800, flags [+],
length: 1500) 86.104.102.16 > 70.84.247.164: udp
21:00:52.941517 IP (tos 0x0, ttl 127, id 28639, offset 16280, flags [+],
length: 1500) 86.104.102.16 > 70.84.247.164: udp 21:00:52.941640 IP (tos
0x0, ttl 127, id 28639, offset 17760, flags [+],
length: 1500) 86.104.102.16 > 70.84.247.164: udp
I have 24 subnets inside a Cisco 3750.
After receiving many packets like these on 3-4 interfaces, Cisco starts
loosing packets and acts abnormal.
I have gathered the output show above from a Linux machine with tcpdump
which acts as a border router.
What I find strange is that there is no port specified (src,dst) and
that the length of the packets is always 1500.
Is there any way to filter something like this on the Cisco switch ?
Is it caused by a virus or by a human ? (I have seen it from 3-4
different interfaces at a time and with 4-6 different destination IPs)
Any help will be greatly appreciated.
Sorry if I have posted this to the wrong list.
