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.
https://exchange.xforce.ibmcloud.com/vulnerabilities/35145
http://www.securityfocus.com/archive/1/471541/100/0/threaded
http://www.portcullis.co.uk/uplds/whitepapers/Having_Fun_With_PostgreSQL.pdf
http://www.mandriva.com/security/advisories?name=MDKSA-2007:188
http://www.leidecker.info/pgshell/Having_Fun_With_PostgreSQL.txt