CVE-2008-3790 in Ruby
Summary
by MITRE
The REXML module in Ruby 1.8.6 through 1.8.6-p287, 1.8.7 through 1.8.7-p72, and 1.9 allows context-dependent attackers to cause a denial of service (CPU consumption) via an XML document with recursively nested entities, aka an "XML entity explosion."
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability described in CVE-2008-3790 represents a critical denial of service flaw affecting the REXML module in multiple versions of the Ruby programming language. This issue specifically targets XML parsing functionality and enables attackers to consume excessive CPU resources through carefully crafted XML documents containing recursively nested entities. The vulnerability affects Ruby versions 1.8.6 through 1.8.6-p287, 1.8.7 through 1.8.7-p72, and extends to early versions of Ruby 1.9, making it a widespread concern across a significant portion of the Ruby ecosystem during that time period.
The technical flaw stems from the REXML module's inadequate handling of XML entity expansion during parsing operations. When processing XML documents containing entities that reference other entities in a recursive manner, the parser fails to implement proper safeguards against infinite expansion loops. This allows an attacker to craft XML documents where entity references create nested expansions that can grow exponentially, leading to massive CPU consumption as the parser attempts to resolve these recursive references. The vulnerability operates at the parsing layer, meaning it can be triggered simply by parsing any XML document containing such malformed entity structures, regardless of the application's intended functionality.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can be exploited to create significant service disruption for applications relying on XML processing. Attackers can cause systems to become unresponsive or consume all available CPU cycles, effectively rendering the application unavailable to legitimate users. This makes the vulnerability particularly dangerous in web applications and services that process user-supplied XML data, as it can be exploited through common attack vectors such as file uploads, API requests, or any input mechanism that accepts XML content. The vulnerability is classified under CWE-400 as an "Uncontrolled Resource Consumption" and aligns with ATT&CK technique T1499.001 for "Network Denial of Service" and T1595.001 for "Network Scanning" when used for reconnaissance purposes.
Mitigation strategies for this vulnerability require immediate action from system administrators and developers. The primary solution involves upgrading to patched versions of Ruby where the REXML module has been updated to include proper entity expansion limits and recursion detection mechanisms. Organizations should also implement XML parsing restrictions at the application level, including setting maximum entity expansion limits, implementing timeouts for XML processing operations, and validating all XML input against strict schemas. Additionally, network-level protections such as rate limiting and input filtering can help reduce the impact of exploitation attempts, while monitoring systems should be configured to detect unusual CPU usage patterns that might indicate exploitation of this vulnerability. The vulnerability demonstrates the importance of input validation and resource limiting in XML processing libraries, as highlighted by industry best practices in secure coding standards and the OWASP Top Ten security risks.