A worm that can compromise systems running the Apache Web server on the FreeBSD operating system is crawling the Internet, but its spread and impact are limited, experts said on Monday.
The worm takes advantage of a known security hole in Apache Web servers by scanning the Internet and installing a backdoor application when it finds a vulnerable Web server. This backdoor allows the attacker to remotely control the system and use it in attacks on other Web servers, according to antivirus software vendor F-Secure in Helsinki.
The open-source Apache server is the most commonly used Web server software, running on 63% of Web sites, according to a survey by Web server analysis firm Netcraft Ltd. of Bath, England.
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However, the reach of the worm, dubbed Scalper by F-Secure, is limited because it only affects Apache on the open-source FreeBSD operating system, said Mikko Hyppönen, research manager at F-Secure.
"It only hits a small fragment of the Apache users," Hyppönen said.
Mike Prettejohn, director at Netcraft, agreed. "FreeBSD is the third most popular platform for Apache after Linux and Solaris," he said.
Hyppönen does not see the worm as a big danger. "The current version is low risk. It is spreading, we can see hits generated by the worm, but it is not widespread. It could infect a measurable portion of the FreeBSD Web server, but that has not happened yet," he said.
Variants of the worm attacking Apache on other platforms may soon surface, Hyppönen said.
"It would be easy to change this worm to work on Linux or any other system. But then, on the positive side, I would think that Apache Web server administrators are diligent in patching, so the spread would not be as big as Code Red, which infected about 200,000 Web sites in two days about a year ago," Hyppönen said.
Indeed, Apache administrators have responded swiftly, with well over 6 million Web sites running on Apache already upgraded to Apache 1.3.26, a version of the software not vulnerable to this attack. However, about 14 million potentially vulnerable sites using Apache remain, Netcraft said in its monthly commentary released on Monday.
Antivirus software vendor Sophos PLC has received a sample of the Apache worm, but has not yet been able to make it work, said Graham Cluley, senior technology consultant at Sophos in Oxford, England.
"At the moment we think it is a bit of a curiosity. We believe it tries to attack FreeBSD machines, but it is so unstable that getting the right configuration to make it work is tough. That of course also will limit the ability to spread," Cluley said.
The flaw in the Apache Web server that the worm exploits affects all versions of Apache 1.2, versions of Apache 1.3 up to 1.3.24 and versions of Apache 2 up to 2.0.36, according to a statement from the Apache Software Foundation released on June 20. The new Apache 1.3.26 and Apache 2.0.39 fix the issue, the Foundation said.
The flaw relates to the way the Web server parses uploaded data and can cause the software to misinterpret the size of incoming chunks of data. It can be exploited by sending a carefully crafted request to the server, said the Foundation, which manages development of the open-source Apache products.
The IDG News Service is a Network World affiliate.
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