CVE-2013-0175 in Grape
Summary
by MITRE
multi_xml gem 0.5.2 for Ruby, as used in Grape before 0.2.6 and possibly other products, does not properly restrict casts of string values, which allows remote attackers to conduct object-injection attacks and execute arbitrary code, or cause a denial of service (memory and CPU consumption) involving nested XML entity references, by leveraging support for (1) YAML type conversion or (2) Symbol type conversion, a similar vulnerability to CVE-2013-0156.
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Analysis
by VulDB Data Team • 01/02/2022
The vulnerability identified as CVE-2013-0175 represents a critical object injection flaw within the multi_xml gem version 0.5.2, which affected Ruby applications including the Grape framework before version 0.2.6. This vulnerability stems from improper handling of string value casting during XML processing, creating a pathway for remote attackers to manipulate application behavior through maliciously crafted XML input. The flaw specifically exploits the gem's support for YAML and Symbol type conversions, enabling attackers to inject arbitrary objects into the application's execution context. The vulnerability operates at the intersection of XML parsing and type conversion mechanisms, where string values are improperly cast without adequate validation or sanitization, creating a direct avenue for code execution and system compromise.
The technical exploitation of this vulnerability leverages the multi_xml gem's ability to automatically convert XML data into Ruby objects using various type conversion methods. When the gem encounters XML data containing nested entities or specially crafted payloads, it attempts to convert string values into Ruby objects using YAML or Symbol conversion mechanisms. This process creates a dangerous injection point where attacker-controlled data can be interpreted as executable code rather than simple string data. The vulnerability is particularly concerning because it allows for both arbitrary code execution and denial of service conditions, making it a dual threat to application security and availability. The flaw is classified under CWE-94, which specifically addresses "Improper Control of Generation of Code" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: Python" and T1203 for "Exploitation for Client Execution" in its exploitation methodology.
The operational impact of CVE-2013-0175 extends beyond simple code execution to encompass significant system stability risks through memory and CPU consumption attacks. Attackers can craft XML payloads that cause excessive memory allocation and processing overhead, leading to denial of service conditions that can overwhelm application servers. The vulnerability's similarity to CVE-2013-0156 demonstrates a pattern of weaknesses in XML parsing libraries where type conversion mechanisms become attack vectors. Applications using affected versions of the multi_xml gem are particularly vulnerable when they process untrusted XML input from external sources, making web services, API endpoints, and any system accepting XML data potential targets. The attack surface is broad since the vulnerability affects not only Grape but potentially other Ruby applications that depend on the multi_xml gem for XML processing, creating widespread exposure across the Ruby ecosystem.
Mitigation strategies for CVE-2013-0175 require immediate patching of affected applications to upgrade to versions of the multi_xml gem that properly validate and sanitize string values during type conversion. Organizations should implement XML input validation and sanitization measures to prevent malicious payloads from reaching the vulnerable parsing layer. The remediation process should include updating the multi_xml gem to version 0.5.3 or later, which contains fixes for the improper casting behavior. Additionally, application developers should implement proper input validation, employ XML parsers with restricted entity expansion capabilities, and consider implementing rate limiting and resource monitoring to detect and prevent denial of service attacks. Security teams should also conduct comprehensive vulnerability assessments to identify all applications using affected versions of the multi_xml gem and establish monitoring procedures to detect potential exploitation attempts. The fix addresses the core issue by implementing proper type validation during XML processing and preventing automatic conversion of user-supplied strings into potentially dangerous Ruby objects through YAML or Symbol mechanisms, thereby eliminating the attack vector that enabled the object injection and code execution capabilities.