A security company has found what appears to be a worm that is exploiting a verified zero-day bug in Sun Microsystems' Solaris 10 and 11.

The Sun Solaris Telnet worm attempts to log into computer systems as the user or administrator, enabling it to execute commands and move on, according to Arbor Network's Security Engineering and Response Team. The security group said it identified the flaw using its Atlas project. The software deploys sensors into service providers' networks to collect data on malware exploits.

"This morning on Atlas, we saw a pair of hosts scanning for Telnet servers," writes Jose Nazario, a software and security engineer with Arbor, in his blog. "While this may seem like a throwback to days gone by, and maybe someone is starting from scratch in their exploit activity, this is related to a recent Solaris bug, specifically CVE-2007-0882 (the telnet "-froot" bug).

The vulnerability -- which the SANS Institute earlier this month called a "major zero-day bug" -- allows hackers to easily gain remote access to computers running the Solaris operating systems. The problem lies in the way Telnet, a network protocol, uses parameters during the authentication process, said Johannes Ullrich in a previous interview with InformationWeek. Ullrich is the CTO for the Internet Storm Center, a cooperative cyberthreat-monitoring and alert system.

By adding simple text to the Telnet command, Ullrich explained that the system will skip asking for a user name and password. If the systems are installed out of the box, they automatically come Telnet-enabled.

Solaris 10 came out in 2005, and more than 7 million users have reportedly registered for it with Sun. Solaris 11, or what Sun code-named Solaris Next, is in beta testing.

A Sun spokesman explained that earlier versions of Solaris 10 had Telnet automatically enabled out of the box, but the latest version does not. He says for both the latest version of Solaris 10 and for the beta version of Solaris 11, users would have to specifically turn Telnet on to enable it. He adds that Sun is recommending that customers use Solaris Secure Shell as the protocol of choice.

Arbor's Nazario says the worm tries to log into systems as the users "lp" or "adm" and then executes several shell commands "to set up shop and keep on truckin'." He calls the attack "very old school."

Joel Esler, a contributor to the Internet Storm Center's online diary, says the center checked its own data and is seeing similar traffic from this worm.

Nazario recommends, "Better yet, just disable Telnet. It's 2007, after all."