Security bugs in Sun Microsystems' telnet service could allow attackers to gain unauthorized access to a system.
The "highly critical" vulnerabilities could enable attackers to gain unauthorized access to a user's system without requiring the user to download exploit code, said Johannes Ullrich, chief research officer at the Sans Institute, which also issued a security advisory.
Attackers could exploit the so-called zero-day vulnerabilities in Solaris 10 and the beta version of Solaris 11 via the telnet service if it is automatically enabled, the advisory said.
Telnet, which dates back to the early days of Unix, was one of the first methods devised to allow system administrators to remotely monitor their networks. The service will usually prompt people for their user name and password. However, security flaws in the operating system could allow an attacker to add additional parameters to connect to the remote telnet server without a user name or password, Ullrich noted.
Once attackers have gained access, they could execute arbitrary commands with the same privileges as the user.
"It's an ancient way to administer systems," Ullrich said. "There's no good reason to enable telnet on Solaris...All the communication with telnet is not encrypted. In recent years, other technologies have replaced it, like (encrypted communications through a secure shell) SSH."
Last month, Sun issued an update to Solaris 10, which now has the SSH enabled by default, said Bob Wientzen, Solaris spokesman for Sun. He added that the company is currently working on a fix for the telnet vulnerabilities.
Sun, in its security advisory, said the vulnerabilities are found in Solaris 10, running on Sparc servers, as well as on x86 servers.
The Sans Institute and Sun said they were not aware of any reports of systems exploited due to the security flaws in the telnet service.
If users must run Solaris with the telnet service enabled, Ullrich recommends using a firewall to limit connections to a user's telnet service. However, he said that while this workaround will prevent direct access to the root account, other accounts on a user's system could still be compromised.