The problem can be corrected by upgrading the affected package to version 1:6.3-025+1ubuntu2.3 (for Ubuntu 4.10), or 1:6.3-046+1ubuntu7.1 (for Ubuntu 5.04). In general, a standard system upgrade is sufficient to effect the necessary changes.
Details follow:
Georgi Guninski discovered that it was possible to construct Vim modelines that execute arbitrary shell commands by wrapping them in glob() or expand() function calls. If an attacker tricked an user to open a file with a specially crafted modeline, he could exploit this to execute arbitrary commands with the user's privileges.