Library items tagged: DDOS

Network time protocol (ntp) servers are regularly being used to reflect and amplify spoofed UDP packets towards the target of a DDoS attack. Attacks are growing in size and frequency and sometimes even cause issues for the organisations hosting the reflectors. Servers offering the 'monlist' command are particularly troublesome and can provide a huge amplification affect.
Anonymous
[1] Microsoft TechNet - Source Address Spoofing: http://www.microsoft.com/technet/security/sourcead.asp [2] ZoneAlarm: http://www.zonelabs.com/ [3] Snort - the Lightweight Network Intrusion Detection System: http://www.snort.org/ [4] Armoring Linux: http://www.spitzner.net/linux.html
Anonymous
In this particular incident, the initial tip-off led directly to the departmental network containing the compromised hosts. This information is not always so readily available, since IP spoofing can also be used to simulate traffic from machines on many different networks. Such a situation could be handled by repositioning the network monitor on the backbone (at M’ in the diagram, for example), and again examining the source MAC addresses of attack packets (but note that performance is likely to be a concern, with monitors dropping traffic at gigabit speeds).
Anonymous
We left the monitor in place for two days, until our log fi le began to grow rapidly indicating a new attack in progress. The following entries are typical of what was observed: [**] IDS253 - DDoS shaft synflood outgoing [**] 06/12-14:30:46.599036 8:0:20:1B:22:A9 -> 0:D0:D3:56:D1:30 type:0x800 len:0x3C 98.76.54.111:1008 -> 12.34.56.78:6666 TCP TTL:30 TOS:0x0 ID:59926 DF
Anonymous
Our monitor is a Linux system running the Snort lightweight intrusion detection system [3]. Demands on hardware are not very high: we use a redundant Pentium 133-based system with two 10/100Mbit/s network interface cards, 128MB memory and 4GB disk space. This allows us to use one interface to access the console, while the other is dedicated to the RSPAN traffic. It is configured with a minimum number of services running and no user accounts [4].
Anonymous
The university network is based on a Gigabit Ethernet backbone, linking together departmental Local Area Networks (LANs) which typically deliver switched 10/100Mbit/s to the desktop. The network is shown diagrammatically in Figure 1. Figure 1: Schematic of the university network
Anonymous
GD/NOTE/001 (01/01) This paper has been contributed by a Janet customer site, and records their experiences in investigating a denial-of-service attack committed using hosts at their site. We are very grateful to them for allowing us to publish this information and hope that it will be useful to others.
Anonymous
Typical Denial of Service abuse (DoS) involves a very large number of connections or packets being directed to the target computer, either from a single source IP address or (Distributed Denial of Service, DDoS) from a number of addresses, possibly a large number and probably in several different networks. Sometimes the effect is to stop the data network working or make it so slow as to interfere with its normal use; sometimes the target is a single machine which also may cease to work or run very slowly.