A working proof-of-concept christened the "Apache Killer" released this week uses an as-yet unpatched flaw in the server software that pounds Apache servers with a distributed denial of service (DDoS) attack--and all it would take is one machine to bring the server to its knees.

The Apache development team late Wednesday issued an alert and workarounds in advance of rolling out a patch for the flaw in Apache HTTPD Web Server 1.3 and 2.X. The Apache Killer lets an attacker use a single PC to wage a denial of service attack against an Apache server.

"By sending specially crafted HTTP requests which include malformed range HTTP header, an attacker can disrupt the normal function of the Web server, thus disallowing legitimate users to receive responses from the Web server," the team's advisory said. "This issue affects all Apache software versions and a patch has not been released yet."

The underlying flaw was apparently first reported on bugtraq in 2007. "It appears due to its lack of sophistication that it did not get much attention by Apache developers and it has remained unpatched all of this time," wrote Kevin Shortt of the SANS Internet Storm Center, who noted that he had not yet tested the proof of concept (PoC), but planned to.

Meanwhile, vendors were stepping forward Thursday announcing their protections against the Apache Killer attack.

Sourcefire said its IPS and open-source Snort technology have been able to detect this flaw for several years and that its vulnerability research team Thursday beefed up that protection with a new rule specific to the Apache Killer.

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