CVE-2015-3907 in Rest Server
Summary
by MITRE
CodeIgniter Rest Server (aka codeigniter-restserver) 2.7.1 allows XXE attacks.
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Analysis
by VulDB Data Team • 10/15/2023
The CVE-2015-3907 vulnerability affects the CodeIgniter Rest Server version 2.7.1, which is a popular PHP framework extension for building RESTful web services. This vulnerability stems from the improper handling of XML data within the application's input processing mechanisms, creating an attack surface that enables XML External Entity processing. The flaw specifically manifests when the application accepts XML payloads without adequate validation or sanitization, allowing malicious actors to inject external entity references that can be processed by the underlying XML parser. This represents a critical security gap in the framework's data handling capabilities, particularly when the server is configured to process XML-formatted requests from external sources.
The technical implementation of this vulnerability involves the XML parser's behavior when encountering external entity declarations within XML documents. When the CodeIgniter Rest Server processes XML input, it fails to properly configure the XML parser to disable external entity resolution, allowing attackers to craft malicious XML payloads containing references to external resources. The attack can be executed by sending specially crafted XML data that includes external entity declarations pointing to internal resources, network locations, or even remote servers. This enables potential information disclosure, denial of service attacks through resource exhaustion, and in some cases, server-side request forgery or remote code execution depending on the server configuration and available attack vectors. The vulnerability aligns with CWE-611, which categorizes improper restriction of XML external entity reference, and represents a classic example of how XML parsing configurations can create security weaknesses when not properly secured.
The operational impact of this vulnerability extends beyond simple data exposure, as it can enable attackers to leverage the server's processing capabilities against internal systems or to extract sensitive information from the host environment. An attacker could potentially access internal network resources, read local files, or perform server-side request forgery attacks by crafting XML payloads that reference internal URLs or files. The vulnerability's severity is amplified in environments where the REST server is exposed to untrusted input sources, as it provides a pathway for attackers to escalate privileges or gain unauthorized access to sensitive data. This type of vulnerability is particularly concerning in web service environments where the server processes data from multiple sources without proper input validation, creating a potential attack vector that can be exploited across various network boundaries.
Organizations should implement immediate mitigations including updating to the latest version of the CodeIgniter Rest Server framework, which contains fixes for the XML parsing behavior. The recommended approach involves configuring the XML parser to disable external entity resolution and to properly validate all incoming XML data before processing. Additionally, implementing proper input sanitization mechanisms, using XML parsers with secure default configurations, and applying network-level restrictions can significantly reduce the attack surface. Security practitioners should also consider implementing web application firewalls to detect and block suspicious XML payloads, and establish monitoring procedures to identify potential exploitation attempts. The vulnerability demonstrates the importance of secure coding practices and proper input validation, aligning with ATT&CK technique T1213 for data exploitation and T1068 for exploit development, making it essential for security teams to address both the immediate patching requirements and implement broader defensive measures against similar vulnerabilities in other components of their web applications.