The Web may be more vulnerable to attack now than at any time previously. That's the stark conclusion of Netcraft's latest monthly survey of Web servers, which expresses concerns over the emergence of serious vulnerabilities in both Microsoft IIS and Apache Web servers over the last month.
These vulnerabilities create a situation where a majority of Internet sites are likely to be accessible to remote exploit, Netcraft, which is not normally associated with alarmist predictions, believes.
On June 11, Microsoft released a trio of advisories, the most serious of which referred to an HTR buffer overflow that could be used to remotely compromise machines running Microsoft-IIS.
Although Netcraft can not explicitly test for the vulnerability without prior permission from the sites, around half of the Microsoft IIS sites on the internet have HTR enabled, making it likely that many will be vulnerable to attack.
Days later it was reported that many versions of the Apache Web server were vulnerable to a buffer overflow because of a flaw in the Web server's chunked encoding mechanism.
If exploited, the flaw could lead to a remote system compromise and exploits are already known to have been been developed for Windows, FreeBSD and OpenBSD. There is an active debate on whether exploits are possible for Linux and Solaris.
Netcraft reports that Apache administrators have reacted quite quickly to the problem, and within a week of first publication, well over 6 million sites have been upgraded to Apache/1.3.26, which addresses the problem.
That still leaves around 14 million potentially vulnerable Apache sites, however.
Netcraft's report says: "With over half of the Internet's web servers potentially vulnerable, conditions are ripe for an epidemic of attacks against both Microsoft-IIS and Apache based sites, and the first worm, targeting sites running Apache on FreeBSD, has been spotted this weekend."
Security watchers monitoring this worm believe its spread has been modest.
Aside from this welcome result, Netcraft notes (quite surprisingly) that worms can have positive effects. It says they can draw administrators' attention to vulnerable servers and - once patched - the server is usually no longer available as a platform for more insidious activity.
Last year, immediately prior to the Code Red worm, Netcraft found that one in six e-commerce sites tested with Microsoft-IIS running had already been successfully compromised, and had a backdoor installed giving an external attacker control over the machine.
"The clear up from Code Red had the positive effect of flushing the majority of these backdoors out of the Internet," it notes. ®