CVE-2013-6460 in Nokogiri Gem
Summary
by MITRE
Nokogiri gem 1.5.x has Denial of Service via infinite loop when parsing XML documents
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Analysis
by VulDB Data Team • 02/04/2024
The CVE-2013-6460 vulnerability represents a critical denial of service flaw discovered in the Nokogiri gem version 1.5.x, which is a widely used ruby library for processing xml and html documents. This vulnerability specifically affects the xml parsing functionality of the gem, creating a condition where maliciously crafted xml documents can trigger an infinite loop during parsing operations. The vulnerability exists within the underlying libxml2 library that Nokogiri depends upon for xml processing, making it particularly concerning given the gem's extensive usage across ruby applications and web frameworks. Security researchers identified that certain xml structures could cause the parser to enter an infinite loop, consuming excessive cpu resources and ultimately leading to system resource exhaustion.
The technical flaw manifests when the xml parser encounters specific malformed or crafted xml documents that contain recursive or self-referential structures within the document hierarchy. This condition causes the parser to continuously iterate through the same xml nodes without proper termination conditions, resulting in an infinite loop that consumes system resources. The vulnerability is categorized under CWE-835, which describes the weakness of infinite loops, and aligns with the broader category of resource exhaustion attacks that fall under the ATT&CK framework's privilege escalation and denial of service tactics. The affected versions of Nokogiri utilize libxml2 versions that lack proper safeguards against such recursive parsing scenarios, making the vulnerability exploitable through simple xml document manipulation.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by attackers to perform resource exhaustion attacks against applications that process untrusted xml input. Web applications using Nokogiri for xml processing, including those handling user-submitted content, xml api responses, or configuration files, become vulnerable to this attack vector. The vulnerability is particularly dangerous in multi-tenant environments or applications with limited resource constraints, where a single malicious xml document can cause complete service unavailability. Attackers can exploit this vulnerability by submitting carefully crafted xml documents to applications that process xml input, leading to high cpu utilization and potential system crashes. The attack requires minimal sophistication and can be automated, making it a preferred vector for denial of service attacks against ruby-based web applications.
Mitigation strategies for CVE-2013-6460 involve immediate version upgrades to Nokogiri 1.6.0 or later, which contain fixes for the underlying libxml2 parsing issues. Organizations should also implement input validation and sanitization measures to filter potentially malicious xml content before processing, though this approach may not fully prevent the vulnerability. Additional protective measures include implementing resource limits and timeouts for xml parsing operations, using alternative xml parsers with better protection mechanisms, and conducting security testing of xml processing components. The fix implemented in newer versions addresses the root cause by adding proper loop detection and termination conditions within the parsing logic, aligning with industry best practices for secure xml processing. Security teams should also monitor for similar vulnerabilities in other xml processing libraries and ensure comprehensive patch management processes are in place to address such issues promptly.