Security analysts are warning about a software flaw that they said could in some cases allow intruders to gain unauthorised access to remote file transfer protocol (FTP) servers.
In an advisory issued Monday, Network Associates' PGP Security division said the problem is related to the "globbing" command used in Unix shells. That essentially acts as a pathname generator, allowing users to search for multiple file names by entering shorthand commands that are then used by the software to search for common patterns.
PGP said its Computer Vulnerability Emergency Response Team found a flaw that allows the pattern expansion done through the glob function to instead be directed to cause various buffer overflows in FTP servers -- a capability that could enable malicious attackers to gain root-level privileges on affected systems.
While potentially dangerous, the problem is said to usually only affect FTP servers that give remote users the ability to create directories on the system hosting the FTP daemon. That will likely restrict the vulnerability's threat, said Greg Shipley, security services director at network and security consulting firm Neohapsis.
"The vast majority of FTP servers out on the Internet don't allow users to create directories," Shipley said. "It could pose a significant threat, but it remains to be seen how many of these FTP servers are going to be affected."
A half-dozen versions of Unix have been confirmed to include vulnerable FTP daemons that could be used to exploit the globbing flaw, according to PGP. The operating systems in question include Hewlett-Packard's HP-UX 11, Silicon Graphics's IRIX 6.5.x and Sun Microsystems's Solaris 8, plus FreeBSD 4.2, OpenBSD 2.8 and NetBSD 1.5.
Since FTP is the primary method of transferring files over the Internet and is used on many servers in default configurations, the problem could allow intruders to take control of the affected servers, PGP said in a separate announcement that was released on Tuesday.