The problem can be corrected by upgrading the affected package to version 2:10.0-5ubuntu0.1 (for Ubuntu 4.10), or 2:10.0-8ubuntu0.1 (for Ubuntu 5.04). In general, a standard system upgrade is sufficient to effect the necessary changes.
Max Vozeler discovered that the the "pstopnm" conversion tool did not use the -dSAFER option when calling ghostscript. This option prohibits file operations and calling commands within PostScript code. This flaw could be exploited by an attacker to execute arbitrary code if he tricked an user (or an automatic server) into processing a specially crafted PostScript document with pstopnm.