Developers of the Apache open-source project today warned users of the popular Web server software that a denial-of-service (DoS) tool is circulating that exploits a bug in the program.
The tool, called "Apache Killer," showed up last Friday in a post to the "Full Disclosure" security mailing list.
Today, the Apache project acknowledged the vulnerability that the attack tool exploits, and said it would release a fix for Apache 2.0 and 2.2 in the next 48 hours.
"A denial of service vulnerability has been found in the way the multiple overlapping ranges are handled by Apache," the group said in a security advisory. According to Apache, all versions in the 1.3 and 2.0 lines are vulnerable to attack.
The group no longer supports the older Apache 1.3.
"An attack tool is circulating in the wild. Active use of this tools has been observed," the advisory stated. "The attack can be done remotely and with a modest number of requests can cause very significant memory and CPU usage on the server."
The bug was not new. Michal Zalewski, a security engineer who works for Google, pointed out that he had brought up the DOS exploitability of Apache more than four-and-a-half years ago.
In lieu of a fix, Apache offered steps administrators can take to defend their Web servers until a patch is available.
According to U.K.-based Netcraft, Apache is the most widely-used Web server software in the world, accounting for 65.2% of all such software currently in use.
Because Apple bundles Apache with Mac OS X -- and maintains the software via its operating system updates -- users running a Mac-based server will have to wait for Apple to deliver a fix.
"It will be interesting to see how Apple rates the bug and how quickly they patch," said Andrew Storms, director of security operations at nCircle, in an interview today via instant messaging.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His e-mail address is firstname.lastname@example.org.