The libxslt support in contrib/xml2 in PostgreSQL 8.3 before 8.3.20, 8.4 before 8.4.13, 9.0 before 9.0.9, and 9.1 before 9.1.5 does not properly restrict access to files and URLs, which allows remote authenticated users to modify data, obtain sensitive information, or trigger outbound traffic to arbitrary external hosts by leveraging (1) stylesheet commands that are permitted by the libxslt security options or (2) an xslt_process feature, related to an XML External Entity (aka XXE) issue.