CVE-2018-11759 in Tomcat
Summary
by MITRE
The Apache Web Server (httpd) specific code that normalised the requested path before matching it to the URI-worker map in Apache Tomcat JK (mod_jk) Connector 1.2.0 to 1.2.44 did not handle some edge cases correctly. If only a sub-set of the URLs supported by Tomcat were exposed via httpd, then it was possible for a specially constructed request to expose application functionality through the reverse proxy that was not intended for clients accessing the application via the reverse proxy. It was also possible in some configurations for a specially constructed request to bypass the access controls configured in httpd. While there is some overlap between this issue and CVE-2018-1323, they are not identical.
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Analysis
by VulDB Data Team • 06/04/2023
The vulnerability identified as CVE-2018-11759 affects the Apache httpd server when used in conjunction with the mod_jk connector for Apache Tomcat. This issue stems from improper path normalization within the connector code that handles requests between the web server and the application server. The flaw exists in versions 1.2.0 through 1.2.44 of the mod_jk connector, creating a significant security gap that allows for unauthorized access to application resources.
The technical implementation of this vulnerability lies in the path normalization process that occurs before URI-worker mapping in the mod_jk connector. When httpd acts as a reverse proxy for Tomcat applications, it processes incoming requests and normalizes the requested paths to match against the configured URI-worker mappings. However, the normalization algorithm fails to properly handle certain edge cases involving path traversal sequences, directory separators, and encoded characters. This incomplete normalization creates opportunities for attackers to manipulate request paths in ways that bypass intended access controls.
The operational impact of this vulnerability is substantial as it enables attackers to exploit the reverse proxy configuration to access application functionality that should remain restricted. When only a subset of Tomcat URLs are exposed through httpd, malicious actors can construct requests that traverse the path normalization logic to reach unintended application endpoints. This allows for information disclosure, unauthorized access to restricted application features, and potential exploitation of application-level vulnerabilities that would otherwise be protected by httpd's access controls. The vulnerability essentially creates a bypass mechanism that undermines the security posture of the reverse proxy configuration.
The security implications extend beyond simple access control bypass to include potential privilege escalation and data exposure scenarios. Attackers can leverage this vulnerability to access application resources that were never intended to be exposed through the reverse proxy, potentially gaining access to administrative interfaces, sensitive data processing endpoints, or other privileged application functionality. The vulnerability's impact is particularly severe in environments where httpd serves as the primary security boundary for Tomcat applications, as it effectively creates a backdoor that allows bypassing the configured access controls.
Mitigation strategies for CVE-2018-11759 primarily focus on upgrading to patched versions of the mod_jk connector where the path normalization logic has been corrected. Organizations should immediately update to mod_jk versions 1.2.45 or later, which contain the necessary fixes for the path normalization edge cases. Additionally, administrators should review their httpd configuration to ensure that access controls are properly implemented and that unnecessary application endpoints are not exposed through the reverse proxy. The fix addresses the core normalization issue while maintaining compatibility with existing configurations. This vulnerability aligns with CWE-22 Path Traversal and CWE-23 Improper Restriction of Operations within the Bounds of a Memory Buffer, and can be categorized under ATT&CK technique T1071.004 Application Layer Protocol: Web Protocols, specifically targeting the exploitation of proxy and reverse proxy configurations for privilege escalation and information gathering activities.