CVE-2017-17042 in YARD
Summary
by MITRE
lib/yard/core_ext/file.rb in the server in YARD before 0.9.11 does not block relative paths with an initial ../ sequence, which allows attackers to conduct directory traversal attacks and read arbitrary files.
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Analysis
by VulDB Data Team • 01/16/2023
The vulnerability identified as CVE-2017-17042 affects the YARD documentation generation tool, specifically within the file handling mechanism located in lib/yard/core_ext/file.rb. This issue represents a classic directory traversal vulnerability that undermines the security controls designed to prevent unauthorized file access within the application's server component. The flaw exists in versions prior to 0.9.11, making all earlier releases susceptible to exploitation by malicious actors who understand how to manipulate file path references.
The technical implementation of this vulnerability stems from inadequate input validation within the file processing logic. When YARD processes file paths, it fails to properly sanitize or validate relative paths that begin with a ../ sequence, which is a standard method for navigating up directory levels in Unix-like filesystems. This allows attackers to craft malicious file requests that can traverse the filesystem hierarchy and access files outside of the intended document root. The vulnerability specifically targets the server functionality of YARD, which is responsible for serving documentation files, making it particularly dangerous in environments where documentation servers are exposed to untrusted users or automated scanning tools.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the capability to access sensitive files that may contain configuration details, source code, or other confidential data stored on the same system. This directory traversal attack vector can be exploited to read system files, application configuration files, or even source code repositories that should remain protected from unauthorized access. The implications are particularly severe in environments where YARD servers are deployed in production systems or where documentation servers are accessible to external users without proper authentication mechanisms.
Security professionals should consider this vulnerability in the context of CWE-22, which specifically addresses improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal. The ATT&CK framework would categorize this as a privilege escalation technique under the T1059 category, specifically focusing on command and scripting interpreter techniques that leverage system-level vulnerabilities. Organizations should prioritize immediate patching of affected YARD installations to version 0.9.11 or later, as this update includes proper path validation that prevents the exploitation of this directory traversal weakness.
Mitigation strategies should include implementing proper input validation at all levels of the application stack, particularly for file path handling functions. Organizations should also consider deploying web application firewalls or security controls that can detect and block suspicious path traversal attempts. Additionally, implementing least privilege principles for YARD server processes and restricting access to documentation servers through proper authentication and authorization mechanisms will significantly reduce the attack surface. Regular security assessments and vulnerability scanning should include checks for similar path traversal vulnerabilities in other components of the application stack to ensure comprehensive protection against these persistent threats.