CVE-2005-4836 in Tomcat
Summary
by MITRE
The HTTP/1.1 connector in Apache Tomcat 4.1.15 through 4.1.40 does not reject NULL bytes in a URL when allowLinking is configured, which allows remote attackers to read JSP source files and obtain sensitive information.
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Analysis
by VulDB Data Team • 06/13/2017
The vulnerability described in CVE-2005-4836 represents a critical security flaw in Apache Tomcat versions 4.1.15 through 4.1.40 that stems from improper input validation in the HTTP/1.1 connector component. This issue specifically manifests when the allowLinking configuration parameter is enabled, creating a pathway for remote attackers to exploit the application server's handling of URL encoding. The flaw exploits a fundamental weakness in how the server processes URL characters, particularly the NULL byte character that should normally be rejected or properly sanitized during request processing. When a malicious user submits a URL containing a NULL byte character while allowLinking is active, the server fails to properly validate this input and instead processes the request as if it were a legitimate path traversal attempt.
The technical implementation of this vulnerability leverages the fact that Apache Tomcat's HTTP connector does not adequately sanitize URL parameters when allowLinking is enabled, which is a configuration option designed to allow symbolic links to be processed within the web application context. This configuration setting, when combined with the absence of NULL byte validation, creates a scenario where an attacker can craft malicious URLs that bypass normal path validation mechanisms. The NULL byte character, which traditionally terminates strings in many programming languages, is not properly filtered out by the Tomcat connector, allowing it to be interpreted as part of the file path. This leads to a path traversal condition where the server attempts to resolve paths that include the NULL byte, potentially allowing access to files that should normally be protected.
The operational impact of this vulnerability is severe and directly affects the confidentiality and integrity of web applications hosted on affected Tomcat versions. Attackers can leverage this flaw to read JSP source files, which often contain sensitive information such as database connection strings, application logic, and other proprietary code that could be used for further exploitation. The vulnerability essentially allows unauthorized access to the server's file system through the web application interface, enabling attackers to extract source code, configuration files, and potentially sensitive data stored within the application's directory structure. This type of information disclosure can lead to complete system compromise, as the extracted source code may contain credentials, business logic, and other sensitive components that can be used for privilege escalation or additional attacks.
The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. This classification indicates that the flaw stems from inadequate validation of file paths and insufficient restrictions on user-provided input. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and credential access through path traversal methods, as attackers can use the information obtained from reading JSP files to gain deeper access to the system. The attack surface is particularly concerning for web applications that store sensitive information in their source code or configuration files, as these files become directly accessible through the vulnerability. Organizations running affected Tomcat versions should immediately implement mitigations including disabling the allowLinking configuration, applying the latest security patches, and implementing proper input validation mechanisms to prevent NULL byte injection in URL processing.
The remediation approach for this vulnerability requires immediate patching of the affected Tomcat versions, as no adequate workarounds exist without compromising application functionality. Organizations should also review their web application configurations to ensure that allowLinking is disabled when not explicitly required, and implement comprehensive input validation at multiple layers of the application stack. Network-based mitigations such as web application firewalls can provide additional protection, though the most effective solution remains the immediate upgrade to patched versions of Apache Tomcat. Security monitoring should be enhanced to detect unusual URL patterns that might indicate exploitation attempts, particularly those involving NULL byte characters or other encoding anomalies that could be indicative of path traversal attacks.