CVE-2019-18978 in rack-cors Gem
Summary
by MITRE
An issue was discovered in the rack-cors (aka Rack CORS Middleware) gem before 1.0.4 for Ruby. It allows ../ directory traversal to access private resources because resource matching does not ensure that pathnames are in a canonical format.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 02/20/2024
The vulnerability identified as CVE-2019-18978 affects the rack-cors gem, a middleware component commonly used in ruby web applications to handle cross-origin resource sharing. This issue represents a directory traversal flaw that enables attackers to access private resources through improper path validation. The vulnerability exists in versions prior to 1.0.4 and stems from the middleware's failure to canonicalize pathnames during resource matching operations, creating a security gap that can be exploited to bypass intended access controls.
The technical flaw resides in the gem's handling of path resolution within its CORS middleware implementation. When processing incoming requests, the middleware does not properly normalize or canonicalize file paths before attempting to match them against configured resource patterns. This allows malicious actors to craft requests containing ../ sequences that traverse directory structures and access files or resources that should otherwise be restricted. The vulnerability specifically impacts how the middleware resolves resource paths, enabling attackers to manipulate the path resolution logic through crafted request parameters or headers that contain directory traversal sequences.
The operational impact of this vulnerability is significant as it can lead to unauthorized access to sensitive resources within applications that rely on rack-cors for CORS handling. Attackers can potentially access private files, configuration data, or internal resources that should be protected from external access. This type of vulnerability can be particularly dangerous in web applications where the middleware is configured to allow access to specific resources but fails to properly validate the paths being accessed. The vulnerability can result in data exposure, privilege escalation, or further exploitation opportunities depending on what sensitive resources are accessible through the affected paths.
This vulnerability maps to CWE-22 Path Traversal and aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, though the primary concern here is the directory traversal aspect rather than DNS specifically. The issue demonstrates poor input validation and path handling practices that are commonly exploited in web application attacks. Organizations using rack-cors middleware should immediately upgrade to version 1.0.4 or later to address this vulnerability. Additionally, administrators should review their CORS configurations to ensure that path matching is properly implemented and that no unnecessary access is granted through overly permissive resource patterns. The fix implemented in version 1.0.4 addresses the core issue by ensuring proper canonicalization of pathnames during resource matching operations, preventing attackers from exploiting directory traversal sequences to access restricted resources.