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Why You Need an Email Exploit Detection Engine

March 21st, 2003

Virus-writers are using increasingly complex and sophisticated techniques in their bid to circumvent anti-virus software and disseminate their viruses.

A case in point was the notorious Nimda virus that used multiple methods to spread itself and was based on an exploit rather than on the virus/Trojan behavior that anti-virus products typically search for. Email security tools must become more sophisticated if such threats are to be blocked before they can cause harm. Anti-virus software, though essential, cannot combat such threats alone; an email exploit detection tool is also necessary.

What is an exploit?

An exploit uses known vulnerabilities in applications or operating systems to execute a program or code. It “exploits” a feature of a program or the operating system for its own use, such as to execute arbitrary machine code, read/write files on the hard disk, or gain illicit access.

What is an email exploit?

An email exploit is an exploit launched via email. An email exploit is essentially an exploit that can be embedded in an email, and executed on the recipient´s machine once the user either opens or receives the email. This allows the hacker to bypass most firewalls and anti-virus products.

Difference between anti-virus software and email exploit detection software

Anti-virus software is designed to detect KNOWN malicious code. An email exploit engine takes a different approach: it analyses the code for exploits that COULD BE malicious. This means it can protect against new viruses, but most importantly against UNKNOWN viruses/malicious code. This is crucial as an unknown virus could be a one-off piece of code, developed specifically to break into your network.

Email exploit detection software analyzes emails for exploits – i.e., it scans for methods used to exploit the OS, email client or Internet Explorer – that can permit execution of code or a program on the user´s system. It does not check whether the program is malicious or not. It simply assumes there is a security risk if an email is using an exploit in order to run a program or piece of code.

In this manner, an email exploit engine works like an intrusion detection system (IDS) for email. The email exploit engine might cause more false positives, but it adds a new layer of security that is not available in a normal anti-virus package, simply because it uses a totally different way of securing email.

Anti-virus engines do protect against some exploits but they do not check for all exploits or attacks. An exploit detection engine checks for all known exploits. Because the email exploit engine is optimised for finding exploits in email, it can therefore be more effective at this job than a general purpose anti-virus engine.

An exploit engine needs to be updated less frequently than an anti-virus engine because it looks for a method rather than a specific virus. Although keeping exploit and anti-virus engines up-to-date involve very similar operations, the results are different. Once an exploit is identified and incorporated in an exploit engine, that engine can protect against any new virus that is based on a known exploit. That means the exploit engine will catch the virus even before the anti-virus vendor is aware of its emergence, and certainly before the anti-virus definition files have been updated to counter the attack. This is a critical advantage, as shown by the following examples that occurred in 2001.

The Lessons of Nimda and BadTrans.B

Nimda and BadTrans.B are two viruses that became highly known worldwide in 2001 because they infected a colossal number of Windows computers with Internet access. Nimda alone is estimated to have affected about 8.3 million computer networks around the world, according to US research firm Computer Economics (November 2001).

Nimda is a worm that uses multiple methods to automatically infect other computers. It can replicate through email using an exploit that was made public months before Nimda hit, the MIME Header exploit. BadTrans.B is a mass-mailing worm that distributes itself using the MIME Header exploit. BadTrans.B first appeared after the Nimda outbreak.

With their highly rapid infection rate, both Nimda and BadTrans.B took anti-virus vendors by surprise. Though the vendors tried to issue definition file updates as soon as they learned about each virus, the virus had already succeeded in infecting a large number of PCs by the time the anti-virus updates were released.

Though both viruses used the same exploit, anti-virus vendors had to issue a separate definition file update for each. In contrast, an email exploit detection engine would have recognized the exploit used and identified the attempt to automatically launch an executable file using the MIME header exploit. As a result, it would have blocked both worms automatically, preventing infection.

Testing for exploit vulnerability

You can easily test whether your email system is vulnerable to the exploit described above and similar email exploits and threats. GFI has set up a testing zone that enables you to determine the susceptibility of your email system to email exploits such as malformed MIME headers, ActiveX exploits, CLSID file names, and more. The tests available on this zone are safe and do not do anything dangerous. They simply detect whether your email system is safeguarded against a number of email-borne threats.

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