An esoteric buffer overflow bug in OpenBSD has been upgraded in importance after it was discovered that, in certain conditions, it could allow a cracker to gain remote access to a server.

Users are recommended to apply a patch to fix the one-byte buffer overflow vulnerability present in an OpenBSD service called ftpd(8). The issue particularly affects non-anonymous FTP (File Transfer Protocol) servers, and administrators of these services are also been encouraged to use more secure transport mechanisms.

The potential risk from the vulnerability is minimised by the fact that to exploit the problem a cracker must have write access to at least one directory.

These factors led to the importance of the bug to be downplayed at first. However the discovery, earlier this week, of a publicly available exploit of the vulnerability led OpenBSD developers to issue a fresh advisory on the issue.

The vulnerability affects OpenBSD versions through 2.8 and NetBSD, though it is not believed to affect FreeBSD.

OpenBSD administrators using ftpd are advised to disable the service and then apply the patch, available here, to their OpenBSD 2.8 source tree. ®