From CAIDA’s “The Spread of the Witty Worm“:
On Friday March 19, 2004 at approximately 8:45pm PST, an Internet worm began to spread, targeting a buffer overflow vulnerability in several Internet Security Systems (ISS) products, including ISS RealSecure Network, RealSecure Server Sensor, RealSecure Desktop, and BlackICE. The worm takes advantage of a security flaw in these firewall applications that was discovered earlier this month by eEye Digital Security. Once the Witty worm infects a computer, it deletes a randomly chosen section of the hard drive, over time rendering the machine unusable. The worm’s payload contained the phrase “(^.^) insert witty message here (^.^)” so it came to be known as the Witty worm.
While the Witty worm is only the latest in a string of self-propagating remote exploits, it distinguishes itself through several interesting features:
- Witty was the first widely propagated Internet worm to carry a destructive payload.
- Witty was started in an organized manner with an order of magnitude more ground-zero hosts than any previous worm.
- Witty represents the shortest known interval between vulnerability disclosure and worm release — it began to spread the day after the ISS vulnerability was publicized.
- Witty spread through a host population in which every compromised host was doing something proactive to secure their computers and networks.
- Witty spread through a population almost an order of magnitude smaller than that of previous worms, demonstrating the viability of worms as an automated mechanism to rapidly compromise machines on the Internet, even in niches without a software monopoly. …
Once Witty infects a host, the host sends 20,000 packets by generating packets with a random destination IP address, a random size between 796 and 1307 bytes, and a destination port. The worm payload of 637 bytes is padded with data from system memory to fill this random size and a packet is sent out from source port 4000. After sending 20,000 packets, Witty seeks to a random point on the hard disk, writes 65k of data from the beginning of iss-pam1.dll to the disk. After closing the disk, the worm repeats this process until the machine is rebooted or until the worm permanently crashes the machine.
Witty Worm Spread
With previous Internet worms, including Code-Red, Nimda, and SQL Slammer, a few hosts were seeded with the worm and proceeded to spread it to the rest of the vulnerable population. The spread was slow early on and then accelerates dramatically as the number of infected machines spewing worm packets to the rest of the Internet rises. Eventually as the victim population becomes saturated, the spread of the worm slows because there are few vulnerable machines left to compromise. Plotted on a graph, this worm growth appears as an S-shaped exponential growth curve called a sigmoid.
At 8:45:18pm PST on March 19, 2004, the network telescope received its first Witty worm packet. In contrast to previous worms, we observed 110 hosts infected in the first ten seconds, and 160 at the end of 30 seconds. The chances of a single instance of the worm infecting 110 machines so quickly are vanishingly small — worse than 10-607. This rapid onset indicates that the worm used either a hitlist or previously compromised vulnerable hosts to start the worm. …
After the sharp rise in initial coordinated activity, the Witty worm followed a normal exponential growth curve for a pathogen spreading in a fixed population. Witty reached its peak after approximately 45 minutes, at which point the majority of vulnerable hosts had been infected. After that time, the churn caused by dynamic addressing causes the IP address count to inflate without any additional Witty infections. At the peak of the infection, Witty hosts flooded the Internet with more than 90Gbits/second of traffic (more than 11 million packets per second). …
The vulnerable host population pool for the Witty worm was quite different from that of previous virulent worms. Previous worms have lagged several weeks behind publication of details about the remote-exploit bug, and large portions of the victim populations appeared to not know what software was running on their machines, let alone take steps to make sure that software was up to date with security patches. In contrast, the Witty worm infected a population of hosts that were proactive about security — they were running firewall software. The Witty worm also started to spread the day after information about the exploit and the software upgrades to fix the bug were available. …
By infecting firewall devices, Witty proved particularly adept at thwarting security measures and successfully infecting hosts on internal networks. …
The Witty worm incorporates a number of dangerous characteristics. It is the first widely spreading Internet worm to actively damage infected machines. It was started from a large set of machines simultaneously, indicating the use of a hit list or a large number of compromised machines. Witty demonstrated that any minimally deployed piece of software with a remotely exploitable bug can be a vector for wide-scale compromise of host machines without any action on the part of a victim. The practical implications of this are staggering; with minimal skill, a malevolent individual could break into thousands of machines and use them for almost any purpose with little evidence of the perpetrator left on most of the compromised hosts.
Posted on May 9th, 2006 by Scott Granneman
Filed under: security