CVE-2009-5135 in Echo
Summary
by MITRE
The Java XML parser in Echo before 2.1.1 and 3.x before 3.0.b6 allows remote attackers to read arbitrary files via a request containing an external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue.
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Analysis
by VulDB Data Team • 01/11/2025
The vulnerability identified as CVE-2009-5135 represents a critical XML External Entity (XXE) flaw within the Java XML parser implementation of the Echo web application framework. This vulnerability affects versions prior to 2.1.1 for the 2.x series and 3.0.b6 for the 3.x series, creating a significant security risk for systems utilizing these outdated versions. The flaw stems from insufficient input validation and improper handling of external entity declarations within XML processing, allowing malicious actors to exploit the system's XML parser functionality.
The technical implementation of this vulnerability occurs when the Echo framework processes XML requests that contain external entity declarations. Attackers can construct malicious requests that include XML external entity references pointing to local files on the server system. When the vulnerable XML parser processes these requests, it automatically resolves the external entity references, effectively enabling unauthorized file access. This occurs because the parser is configured to accept and process external entity declarations without proper restrictions or validation mechanisms. The vulnerability specifically leverages the XML parser's capability to resolve external entities, which is a legitimate feature for legitimate XML processing but becomes dangerous when exploited by malicious actors.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the ability to access arbitrary files on the server filesystem. This can lead to exposure of sensitive configuration files, database credentials, application source code, and other confidential data stored locally on the system. The attack vector is particularly concerning because it requires minimal privileges to execute successfully, as the vulnerability exists within the XML processing layer itself. An attacker needs only to craft a malicious XML request containing external entity declarations that reference local files, then submit this request to the vulnerable Echo application. The vulnerability is classified under CWE-611 as "Improper Restriction of XML External Entity Reference" and aligns with ATT&CK technique T1213.002 for "Data from Information Repositories" and T1566.001 for "Phishing with Social Engineering".
Mitigation strategies for this vulnerability require immediate remediation through version updates to patched releases of the Echo framework. Organizations should upgrade to versions 2.1.1 or 3.0.b6 and later, which contain proper XML parser configuration to prevent external entity resolution. Additionally, administrators should implement XML parser hardening measures such as disabling external entity resolution entirely, implementing strict input validation for XML content, and configuring proper access controls for file system resources. Network-level protections including firewall rules and web application firewalls can provide additional defense-in-depth measures. Security monitoring should be enhanced to detect unusual XML processing patterns and unauthorized file access attempts. The vulnerability demonstrates the critical importance of proper XML security configuration and highlights the necessity of keeping third-party libraries updated to prevent exploitation of known vulnerabilities. Organizations should also conduct comprehensive vulnerability assessments to identify other potentially affected systems and ensure that XML processing components are properly configured to prevent similar XXE attacks.