CVE-2014-8090 in Ruby
Summary
by MITRE
The REXML parser in Ruby 1.9.x before 1.9.3 patchlevel 551, 2.0.x before 2.0.0 patchlevel 598, and 2.1.x before 2.1.5 allows remote attackers to cause a denial of service (CPU and memory consumption) a crafted XML document containing an empty string in an entity that is used in a large number of nested entity references, aka an XML Entity Expansion (XEE) attack. NOTE: this vulnerability exists because of an incomplete fix for CVE-2013-1821 and CVE-2014-8080.
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Analysis
by VulDB Data Team • 05/10/2026
The vulnerability identified as CVE-2014-8090 represents a critical denial of service flaw affecting Ruby's REXML parser across multiple versions including 1.9.x before 551, 2.0.x before 598, and 2.1.x before 5.5. This vulnerability specifically targets XML Entity Expansion attacks where malicious actors can craft specially designed XML documents to consume excessive system resources. The flaw occurs when an empty string is included in an entity that is subsequently referenced numerous times within deeply nested structures, creating a cascading effect that rapidly depletes CPU cycles and memory resources. The vulnerability is particularly insidious because it exploits the parser's handling of entity references, which are legitimate XML features used for defining reusable content within documents. Attackers can leverage this weakness by constructing XML documents that contain recursive entity references with empty strings, causing the parser to enter infinite loops or consume disproportionate computational resources during processing.
This vulnerability directly relates to CWE-400, which categorizes issues involving unchecked resource consumption, and more specifically aligns with CWE-128, which addresses issues in XML parsers related to entity expansion. The attack pattern follows established methodologies described in the MITRE ATT&CK framework under the technique T1499.004 for network denial of service attacks, where adversaries target application parsing logic to exhaust system resources. The vulnerability's classification as an incomplete fix for previous CVE-2013-1821 and CVE-2014-8080 highlights the complexity of addressing XML parsing security issues and demonstrates how remediation efforts can sometimes introduce new attack vectors. The root cause stems from insufficient validation of entity expansion limits within the REXML parser implementation, where the parser fails to properly detect and terminate excessive nested entity references that could lead to resource exhaustion.
The operational impact of CVE-2014-8090 extends beyond simple service disruption to potentially compromise entire application availability. When exploited, the vulnerability allows attackers to consume CPU resources at an exponential rate, potentially causing system slowdowns, application crashes, or complete service unavailability. Memory consumption increases rapidly as the parser attempts to resolve nested entity references, leading to potential out-of-memory conditions that can affect not just the targeted application but also the underlying operating system. The attack is particularly dangerous in web applications that process user-supplied XML data, as it can be triggered through various input vectors including file uploads, API endpoints, or web form submissions. Organizations running Ruby applications that accept XML input from untrusted sources are particularly vulnerable, as the attack requires minimal privileges and can be executed through standard network-based means without requiring authentication or specialized tools.
Mitigation strategies for CVE-2014-8090 should focus on immediate version upgrades to patched Ruby releases, specifically ensuring Ruby 1.9.3 patchlevel 551, 2.0.0 patchlevel 598, or 2.1.5 and later versions. Organizations should implement strict XML input validation and parsing limits, including setting maximum entity expansion depths and preventing recursive entity references in application code. Network-level protections such as rate limiting and input filtering can provide additional defense-in-depth measures, while monitoring systems should be configured to detect unusual CPU and memory consumption patterns that might indicate exploitation attempts. The implementation of XML parsers with built-in entity expansion limits and proper resource accounting should be prioritized in future application development. Security teams should conduct comprehensive vulnerability assessments to identify all Ruby applications within their environment that might be exposed to this vulnerability, particularly those processing external XML data, and ensure that all systems are updated with appropriate patches to prevent exploitation.