If users have put off patching their Apache Web servers against the vulnerability discovered on Monday, they should wait no longer, as an exploit to attack the security hole is now circulating on the Internet, according to Oliver Friedrichs, director of engineering at SecurityFocus.
The exploit -- a tool which makes attacking a vulnerability easier -- was posted to the Bugtraq security e-mail list on Wednesday, Friedrichs said.
The existence of an exploit "makes the possibility of a worm that targets these systems more likely", he said.
The vulnerability, announced on Monday by Internet Security Systems and then expanded upon by the Apache Software Foundation, could allow an attacker to take control of an affected Web server. Because of a flaw in the way Apache handles uploads, an attacker could send a specially formed request to the server and cause it to deny service to legitimate users or take the system over, both groups said.
More than 60 per cent of the Web servers on the Internet use Apache, according to data from Web server monitoring firm Netcraft.
CERT/CC (Computer Emergency Response Team/Coordination Center), a federally funded computer security body located at Pittsburgh's Carnegie Mellon University, and Internet Security Systems both updated their advisories on the vulnerability after the release of the exploit, urging users to patch their systems.
Despite the presence of an exploit, SecurityFocus "hasn't seen increased attack activity" focused at Apache systems, Friedrichs said. SecurityFocus monitors the networks of over 9,000 companies in over 145 countries for security data and then aggregates it to create a picture of global, regional and industry-specific Internet security.
The dearth of attacks isn't surprising to Friedrichs, as there is usually a one to two-week period between vulnerability announcements and attacks, he said.
Though the exploit released on Wednesday only attacks Apache installations running on the OpenBSD operating system, "it's not a monumental task for someone to modify it" to work with other operating systems, he said.
Users should patch their systems immediately and check with their vendors for more information, Friedrichs said.
"People should be making the patching of their Apache servers a high priority," he said.