Common Vulnerabilities and Exposures assigned an identifier CVE-2007-3280 to the following vulnerability: The Database Link library (dblink) in PostgreSQL 8.1 implements functions via CREATE statements that map to arbitrary libraries based on the C programming language, which allows remote authenticated superusers to map and execute a function from any library, as demonstrated by using the system function in libc.so.6 to gain shell access. References: http://www.securityfocus.com/archive/1/archive/1/471541/100/0/threaded http://www.leidecker.info/pgshell/Having_Fun_With_PostgreSQL.txt http://www.portcullis.co.uk/uplds/whitepapers/Having_Fun_With_PostgreSQL.pdf
Red Hat does not consider this do be a security issue. Ability of the superuser to execute code on behalf of database server is intended feature and imposes no security threats as superuser account is restricted to database administrator.