Sun has patched a critical bug that could let attackers snatch control of Solaris 10 systems by using the Telnet daemon.

The fix comes just three days after exploit code for the zero-day vulnerability was posted to a security Web site. "Big round of applause for Sun owning up to the mistake and fixing it quickly," said Dave Maynor, chief technology officer at Atlanta-based Errata Security, in a blog.

A Sun security researcher owned up to the foul-up of leaving Telnet vulnerable. "Yes, this was an almighty [mess] up and should not have happened," Alan Hargreaves, an engineer in Sun's support group who wrote the initial patch, said in his own blog. "It did happen. Let's move on."

Although Hargreaves' patch fixed the bug, security organizations, including US-CERT and Errata Security, recommended that Solaris users also disable the Telnet daemon - or if they've turned it off, leave it off - using the command: # svcadm disable svc:/network/telnet:default.

The patch can be downloaded from Sun's support site.