CVE-2017-7675 in Tomcat
Summary
by MITRE
The HTTP/2 implementation in Apache Tomcat 9.0.0.M1 to 9.0.0.M21 and 8.5.0 to 8.5.15 bypassed a number of security checks that prevented directory traversal attacks. It was therefore possible to bypass security constraints using a specially crafted URL.
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Analysis
by VulDB Data Team • 11/06/2019
The vulnerability CVE-2017-7675 represents a critical security flaw in Apache Tomcat's HTTP/2 implementation that affected versions ranging from 9.0.0.M1 through 9.0.0.M21 and 8.5.0 through 8.5.15. This directory traversal vulnerability emerged from the HTTP/2 protocol handling mechanism within the Tomcat server, specifically in how it processed and validated URLs. The flaw allowed attackers to circumvent security restrictions that normally prevent unauthorized access to directory structures, effectively enabling malicious users to access files and directories that should have been protected by the application's security controls. The vulnerability stems from insufficient validation of HTTP/2 frames and their associated path components, creating a pathway for attackers to manipulate request processing and gain unauthorized access to sensitive resources.
The technical implementation of this vulnerability resides in the HTTP/2 request processing logic where the Tomcat server failed to properly validate the path components of incoming requests. When HTTP/2 requests were processed, the server did not adequately check for directory traversal sequences such as .. or %2e%2e that could be embedded within the request path. This failure allowed attackers to craft URLs containing these traversal sequences that would be interpreted by the server as legitimate requests to access parent directories or specific files outside the intended application scope. The vulnerability was particularly dangerous because HTTP/2's binary framing protocol and its handling of pseudo-headers could be manipulated to bypass the traditional URL validation mechanisms that typically protect against such attacks. This issue falls under the CWE-22 category of Improper Limitation of a Pathname to a Restricted Directory, commonly known as Path Traversal, which is a well-documented vulnerability pattern in software security.
The operational impact of CVE-2017-7675 extends beyond simple unauthorized file access, potentially enabling attackers to compromise entire application servers through directory traversal attacks. An attacker could exploit this vulnerability to access sensitive files such as configuration files, source code, database credentials, or other confidential information stored on the server. The implications are particularly severe in environments where Tomcat serves web applications with sensitive data, as this vulnerability could lead to complete system compromise. The attack vector is particularly concerning because HTTP/2 is increasingly being adopted in modern web applications, and the vulnerability affects multiple versions of Tomcat, creating widespread exposure across numerous production environments. The vulnerability also aligns with ATT&CK technique T1083 which focuses on discovering file and directory permissions, making it a significant threat for attackers seeking to enumerate and access protected resources within the application environment.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to patched versions of Apache Tomcat, specifically versions 9.0.0.M22 and 8.5.16 or later, which contain the necessary fixes for the HTTP/2 path validation logic. Additionally, administrators should consider implementing network-level controls and web application firewalls to monitor and block suspicious URL patterns that could indicate exploitation attempts. The patch addresses the core issue by strengthening the validation of path components within HTTP/2 requests and ensuring that directory traversal sequences are properly rejected during request processing. Security teams should also conduct comprehensive audits of their Tomcat deployments to identify any instances running vulnerable versions and ensure that all HTTP/2 enabled services are properly secured. The remediation process should include thorough testing of the patched versions to ensure that legitimate application functionality remains intact while the security vulnerability is effectively addressed.