CVE-2013-6461 in Nokogiri
Summary
by MITRE
Nokogiri gem 1.5.x and 1.6.x has DoS while parsing XML entities by failing to apply limits
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 02/04/2024
The vulnerability identified as CVE-2013-6461 affects the Nokogiri gem version 1.5.x and 1.6.x, representing a significant denial of service weakness in XML entity parsing capabilities. This flaw manifests when the gem processes XML documents containing maliciously crafted entity references that can trigger excessive resource consumption during parsing operations. The vulnerability stems from insufficient input validation and lack of proper entity limit enforcement within the XML processing pipeline, allowing attackers to craft specially formatted XML documents that can cause the parser to consume excessive memory and processing cycles. The issue is particularly concerning as Nokogiri is widely used across numerous Ruby applications and web frameworks, making this vulnerability potentially exploitable across a broad attack surface.
The technical implementation of this vulnerability involves the improper handling of XML entities during document parsing, where the parser fails to enforce reasonable limits on entity expansion and recursion depth. When processing XML documents with deeply nested or cyclic entity references, the parser continues to expand entities without bounds, leading to exponential memory consumption and potential system resource exhaustion. This behavior aligns with CWE-400, which classifies the weakness as an unchecked resource consumption vulnerability, specifically addressing the lack of proper resource limits in parsing operations. The vulnerability exploits the fundamental XML parsing mechanism where entity references can reference other entities, creating potential for unbounded expansion that the parser should normally prevent through configured limits.
The operational impact of CVE-2013-6461 extends beyond simple service disruption to potentially enable more sophisticated attack vectors when combined with other weaknesses. Applications utilizing affected Nokogiri versions become vulnerable to resource exhaustion attacks that can cause application crashes, system slowdowns, or complete service unavailability. Attackers can leverage this vulnerability by submitting malicious XML payloads to applications that process user-supplied XML data, such as web services, content management systems, or any application that accepts XML input. The attack requires minimal privileges and can be executed through standard XML processing interfaces, making it particularly dangerous in environments where XML processing occurs without proper input sanitization. This vulnerability directly maps to ATT&CK technique T1499.004, which describes resource exhaustion attacks targeting application availability.
Mitigation strategies for this vulnerability primarily focus on immediate version updates to Nokogiri 1.6.1 or later, where the parser implementation was corrected to enforce proper entity limits and recursion depth controls. System administrators should also implement input validation and sanitization measures, particularly for XML data processing pipelines, to prevent malicious XML documents from reaching the vulnerable parser. Additional protective measures include implementing rate limiting on XML processing requests, configuring memory limits for XML parsing operations, and monitoring for unusual resource consumption patterns that might indicate exploitation attempts. Organizations should also consider implementing XML schema validation and restricting the types of entities that can be referenced within their XML processing environments to further reduce the attack surface. The remediation approach aligns with security best practices outlined in OWASP Top 10 2021, specifically addressing the prevention of resource exhaustion vulnerabilities through proper input validation and resource management controls.