CVE-2008-1891 in Ruby
Summary
by MITRE
Directory traversal vulnerability in WEBrick in Ruby 1.8.4 and earlier, 1.8.5 before 1.8.5-p231, 1.8.6 before 1.8.6-p230, 1.8.7 before 1.8.7-p22, and 1.9.0 before 1.9.0-2, when using NTFS or FAT filesystems, allows remote attackers to read arbitrary CGI files via a trailing (1) + (plus), (2) %2b (encoded plus), (3) . (dot), (4) %2e (encoded dot), or (5) %20 (encoded space) character in the URI, possibly related to the WEBrick::HTTPServlet::FileHandler and WEBrick::HTTPServer.new functionality and the :DocumentRoot option.
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Analysis
by VulDB Data Team • 08/08/2019
The vulnerability described in CVE-2008-1891 represents a critical directory traversal flaw within WEBrick's HTTP server implementation in Ruby versions prior to specific patch releases. This vulnerability specifically affects systems utilizing NTFS or FAT filesystems where the web server's document root is configured through the WEBrick::HTTPServer.new functionality with the :DocumentRoot option. The flaw arises from insufficient input validation in the WEBrick::HTTPServlet::FileHandler component that processes incoming HTTP requests. Attackers can exploit this weakness by appending specific character sequences to URIs, including trailing plus signs, encoded plus characters, dots, encoded dots, or encoded spaces, which allows them to bypass normal file access restrictions and gain unauthorized access to CGI files and other sensitive resources within the server's document root.
The technical implementation of this vulnerability stems from how WEBrick handles URI normalization and file path resolution on NTFS and FAT filesystems where directory traversal attacks can be executed through the manipulation of path separators and special characters. When a client requests a resource, the server's file handler processes the URI and attempts to resolve the requested file path. However, the implementation fails to properly sanitize or canonicalize the URI before performing file system operations, allowing attackers to craft malicious requests that cause the server to traverse directories beyond the intended document root. This behavior is particularly dangerous on Windows systems where NTFS and FAT filesystems handle path resolution differently than Unix-like systems, creating opportunities for attackers to access files they should not be able to reach through normal web browsing operations.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more severe attacks including arbitrary code execution through CGI scripts, data theft from sensitive configuration files, and complete system compromise when combined with other vulnerabilities. The vulnerability affects multiple Ruby versions simultaneously, making it widespread across many deployed web applications that rely on WEBrick for development or lightweight production environments. Organizations using Ruby-based applications with WEBrick servers are at risk of unauthorized access to their web content, application source code, database credentials, and other sensitive information stored within the server's accessible directories. The attack vector requires no authentication and can be executed remotely, making it particularly dangerous for applications deployed in environments where security controls are minimal or absent.
Mitigation strategies for CVE-2008-1891 should focus on immediate version upgrades to patched Ruby releases, specifically targeting Ruby 1.8.5-p231, 1.8.6-p230, 1.8.7-p22, and 1.9.0-2 or later versions that contain the necessary fixes for the directory traversal vulnerability. Organizations should also implement additional defensive measures including input validation at the web server level, proper configuration of document root directories to limit access to only necessary files, and deployment of web application firewalls that can detect and block suspicious URI patterns. The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and maps to ATT&CK techniques including T1059 for command and scripting interpreter and T1566 for credential access through exploitation of web application vulnerabilities. Network segmentation and monitoring should be implemented to detect potential exploitation attempts, and regular security audits should verify that no vulnerable systems remain operational within the organization's infrastructure.