THE ART OF COMPUTER VIRUS RESEARCH AND DEFENSE [Electronic resources] نسخه متنی

Figure 9.19. The accidental interaction of a worm infected with a file infector virus.

³⁶. Because several antivirus softwares had problems detecting the password-protected attachments reliably, "traveler viruses" could take advantage of this accidental cooperation.

A form of cooperation also exists with the previously mentioned W32/Borm creation, which infects BackOrifice-compromised systems. W32/Borm does not attempt to kill Back Orifice; it simply takes advantage of compromised systems to propagate. Similarly, the aforementioned Mydoom had a backdoor that was utilized by the Doomjuice worm to spread itself.

With macro and script viruses, "body snatching" attacks often occur. Two or more script or macro viruses might form a new creation as they accidentally propagate each other's code.

9.8.2. Competition

Competition between malicious codes was also experienced among computer viruses. Several viruses attack other viruses and disinfect them from the systems that they have compromised. An example of this is the Den_Zuko boot virus³⁷, which disinfects the Brain virus. These viruses are often called "benefical viruses" or "antivirus" viruses.

Antiworm computer worms started to become more popular in 2001 with the appearance of the CodeRed worm and the counterattacking, CodeGreen. (However, antiworm worms had been experienced previously on other platforms, such as Linux.)

Because IIS could be exploited more than once, CodeGreen could easily attack CodeRed-infected systems. The worm sent a similarly malformed GET request to the remote target nodes to CodeRed, which had in front the message shown in Listing 9.9.

Listing 9.9. The Front of a CodeGreen GET Request

GET /default.ida?Code_Green_<I_like_the_colour-_-><AntiCodeRed-
CodeRedIII-IDQ_Patcher>_V1.0_beta_written_by_'Der_HexXer'-
Wuerzburg_Germany-_is_dedicated_to_my_sisterli_'Doro'.
Save_Whale_and_visit_<www.buhaboard.de>_and_www.buha-security.de

The worm also carried the following messages shown in Listing 9.10.

Listing 9.10. Other Messages of the CodeGreen Worm

HexXer's CodeGreen V1.0 beta CodeGreen has entered your system
it tried to patch your system and
to remove CodeRedII's backdoors
You may uninstall the patch via
SystemPanel/Sofware: Windows 2000 Hotfix [Q300972]
get details at "www.microsoft.com".
visit "www.buha-security.de

CodeGreen removed the CodeRed infections from systems and also removed the backdoor components of other CodeRed variants. Furthermore, it downloaded and installed patches to close the vulnerability.³⁸ worm was developed with a vampire attack. I decided to call this kind of attack a "vampire" based on the Core War vampire attack. Vampire warriors can steal their enemies' souls (see Chapter 1, "Introduction to the Games of Nature," for details).

Gaobot.AJS is a vampire because it attacks Sasser when the two worms are on the same machine. Instead of simply killing Sasser, Gaobot.AJS modifies Sasser's code in a very tricky way. As a result of the modification, Sasser can still scan for new targets and even exploit them successfully. However, when Sasser connects to its shellcode on the compromised system to instruct it to download and execute a copy of Sasser via FTP, the code modifications of Gaobot.AJS will get control. In turn, Gaobot.AJS sends commands to Sasser's shellcode on the remote machine and instructs it to download a copy of Gaobot.AJS's code instead of Sasser's. Furthermore, Gaobot closes the connection to the remote machine so Sasser cannot propagate but is used as a Gaobot propagation agent in a parasitic manner.

Another gripping example is the W32/Dabber worm, which appeared right after Sasser. As mentioned, Sasser's shellcode is instructed to download a copy of Sasser via FTP. On the attacker system, Sasser implements a crude FTP server. However, this routine of Sasser had a simple buffer overflow vulnerability that could be exploited. (Indeed, worms can have their own vulnerabilities!) Dabber was released to exploit Sasser's vulnerability to propagate itself. It scans for targets that were compromised by Sasser and attempts to connect to Sasser's vulnerable "FTP server" to exploit it successfully.

It is expected that competitions between malicious programs will become more and more common in the future.

9.8.3. The Future: A Simple Worm Communication Protocol?

Although increased competition among malicious programs is likely, it also makes sense for attackers to invest in cooperating techniques. For example, computer worms could use a special protocol such as simple worm communication protocol (SWCP) to exchange information, as well as plug-ins ("genes") among different families of computer worms that support SWCP. Computer worms could swap payloads, exchange information about systems to attack, or even collect e-mail addresses and share them with the other worms that occasionally communicate using SWCP. I highly anticipate that such techniques will appear in the very near future.³⁹ to cross their genomes to produce offspring, which can evolve or devolve. The closest currently known example of accidentally "sexually reproducing" computer viruses can be found in macro viruses which occasionally swap, or snatch their macros ("genes") as discussed in Chapter 3, "Malicious Code Environments,". However, specifically written binary viruses could possibly demonstrate similar behavior that would lead to further evolution in computer viruses on their own.