A mass attack ongoing for the past month against Linux Apache Web servers has become increasingly successful because its break-in method makes use of an automated password and installation process, according to a security researcher monitoring its progress.

Don Jackson, senior security researcher at SecureWorks, says the attack, which was first thought to have compromised several hundred Web sites, has hit at least 10,000. He says the attack relies on making use of stolen passwords to Linux Apache servers by automating the installation process to force it to serve up attacks against vulnerabilities on Windows clients.

“The Web server ends up serving up vulnerabilities from 2006 related to Windows malware,” Jackson says. “The whole attack is very mysterious. It’s based on a botnet but it doesn’t match the Russian and Chinese groups and may be Western Europe or North American.”

The attack, which makes use of the well-known Rbot and Sdbot malware, targets at least nine software vulnerabilities associated with QuickTime exploits, AOL SuperBuddy and Yahoo! Messenger to try and compromise Windows-based desktops. SecureWorks says most antivirus vendors can detect the malware.

The ingenuity is that the attacker has managed to install code that modifies Apache memory to monitor requests and inject the script tag, script contents or the Rbot executable, according to SecureWorks. Some Linux Apache network managers are finding it hard to clean their servers of the attack code, he notes.

For the infection to work, the dynamic-module loading feature in Linux Apache must be enabled, which is the default. To protect against the attack, Linux Apache network managers should disable “dynamic module,” Jackson says, adding,  “However, this isn’t a fix for everyone” because some servers actively depend on this feature.

Jackson says he is aware there is “proof-of-concept code” for a similar attack based on automated stolen-password and malware installation for Microsoft’s Internet Information Server, but he hasn’t seen it come into broad use the way the automated Linux Apache server attack is spreading.