CVE-2011-3744 in HTML Purifier
Summary
by MITRE
HTML Purifier 4.2.0 allows remote attackers to obtain sensitive information via a direct request to a .php file, which reveals the installation path in an error message, as demonstrated by tests/PHPT/Reporter/SimpleTest.php and certain other files.
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Analysis
by VulDB Data Team • 01/17/2018
The vulnerability identified as CVE-2011-3744 affects HTML Purifier version 4.2.0 and represents a sensitive data exposure issue that fundamentally undermines the security posture of applications relying on this library. This flaw manifests when remote attackers can directly access specific php files within the application's directory structure, particularly targeting test files such as tests/PHPT/Reporter/SimpleTest.php, which inadvertently disclose the system's installation path through error messages. The vulnerability stems from inadequate error handling mechanisms within the library's test infrastructure, where sensitive filesystem information becomes exposed during error conditions rather than being properly sanitized or suppressed. This type of information disclosure vulnerability falls under the CWE-200 category, which specifically addresses the exposure of sensitive information to an unauthorized actor, and represents a classic example of how seemingly innocuous test components can become attack vectors when deployed in production environments.
The technical implementation of this vulnerability exploits the library's error reporting mechanisms to reveal directory traversal paths and system file structures. When the targeted .php files are accessed directly rather than through the intended application interface, the system generates error messages that contain the full filesystem path where HTML Purifier is installed. This occurs because the test infrastructure lacks proper input validation and error handling that would normally prevent such information from being exposed to external parties. The vulnerability is particularly concerning because it allows attackers to gather intelligence about the target system's architecture, potentially enabling more sophisticated attacks such as path traversal exploits or targeted attacks against specific system components. From an operational perspective, this vulnerability directly violates the principle of least privilege and information hiding, as it provides attackers with valuable reconnaissance data that could be used to craft more effective attacks against the system.
The impact of this vulnerability extends beyond simple information disclosure, as the exposed installation paths can serve as foundational intelligence for attackers planning more complex penetration testing or exploitation attempts. The presence of such path information in error messages creates opportunities for attackers to understand the application's deployment structure, potentially revealing shared hosting configurations, directory permissions, or other system characteristics that could be leveraged in subsequent attack phases. This vulnerability aligns with several ATT&CK techniques including T1083 (File and Directory Discovery) and T1068 (Exploitation for Privilege Escalation), as the information disclosure enables attackers to gather system information that can be used to identify potential privilege escalation targets or to refine their attack vectors. Organizations deploying HTML Purifier 4.2.0 should consider this vulnerability as a critical component in their overall security posture, particularly in environments where security through obscurity is not sufficient to protect against determined adversaries.
The recommended mitigation strategies for this vulnerability involve multiple layers of defense to address both the immediate exposure and prevent similar issues in the future. The primary solution requires updating to a patched version of HTML Purifier that properly handles error messages and prevents the exposure of installation paths in error conditions. Additionally, administrators should ensure that test and development files are not accessible from production environments, implementing proper access controls and directory permissions to prevent direct access to internal library components. Network-level defenses such as web application firewalls can also be configured to detect and block requests targeting known vulnerable paths, while proper logging and monitoring should be implemented to detect attempts to access these sensitive files. The vulnerability also highlights the importance of proper error handling practices and the need for security testing that includes reviewing error message content and ensuring that no sensitive system information is exposed during error conditions. Organizations should also consider implementing automated security scanning tools that can identify similar information disclosure vulnerabilities in their codebases and dependencies, as this type of issue can often be found in other libraries and applications beyond just HTML Purifier.