CVE-2012-6685: 
Ruby vulnerability analysis and mitigation

Nokogiri before version 1.5.4 was found to contain an XML eXternal Entity (XXE) vulnerability. The issue was discovered and reported by Felix Groebert of Google, and was assigned CVE-2012-6685. The vulnerability affected the XML parsing functionality in Nokogiri, a popular Ruby gem for parsing HTML, XML, and SAX documents (Debian Tracker, NVD).

The vulnerability allowed external XML entities to be specified in specially crafted XML documents. When such documents were parsed, they could trigger connections to specified URLs, potentially leading to unauthorized access of resources. The issue was particularly concerning because it could be exploited through both network-based and local file URLs (GitHub Issue).

The vulnerability could allow attackers to trigger connections to internal network resources or access local files through specially crafted XML documents. This could potentially lead to information disclosure or unauthorized access to resources on systems processing XML content with affected Nokogiri versions (Red Hat Bugzilla).

The vulnerability could be exploited by providing a specially crafted XML document containing external entity references. A proof of concept demonstrated that when parsing such documents, the parser would make connections to specified URLs, including both HTTP URLs and local file system references (GitHub Issue).

The vulnerability was addressed in Nokogiri version 1.5.4 through the introduction of a 'nonet' option to disable external connections. However, it was noted that local file URLs could still be used to exploit the vulnerability. A complete fix was later implemented in version 1.6.4 by updating to libxml2 2.9.0 (Nokogiri Changelog).