CVE-2021-22867 in GitHub
Summary
by MITRE • 07/15/2021
A path traversal vulnerability was identified in GitHub Enterprise Server that could be exploited when building a GitHub Pages site. User-controlled configuration options used by GitHub Pages were not sufficiently restricted and made it possible to read files on the GitHub Enterprise Server instance. To exploit this vulnerability, an attacker would need permission to create and build a GitHub Pages site on the GitHub Enterprise Server instance. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.1.3 and was fixed in 3.1.3, 3.0.11, and 2.22.17. This vulnerability was reported via the GitHub Bug Bounty program.
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Analysis
by VulDB Data Team • 07/18/2021
This vulnerability represents a critical path traversal flaw in GitHub Enterprise Server's GitHub Pages functionality that demonstrates how insufficient input validation can lead to unauthorized file access within server environments. The issue specifically manifested when users with appropriate permissions attempted to build GitHub Pages sites, as the system failed to properly sanitize user-controlled configuration parameters that were subsequently processed by the underlying file system operations. This weakness created an exploitable condition where malicious actors could potentially access sensitive files on the server instance through carefully crafted page configurations, bypassing normal access controls and file system restrictions that should have protected system resources.
The technical implementation of this vulnerability stems from inadequate sanitization of user inputs within the GitHub Pages build process, which aligns with common CWE classifications for path traversal attacks. When users created GitHub Pages sites, the system accepted configuration options without proper validation, allowing attackers to inject malicious file paths that would be processed by the server's file system operations. This flaw operates at the intersection of input validation and privilege escalation, as it requires legitimate user access to create pages but then allows that access to be leveraged for unauthorized file reading. The vulnerability's exploitation pathway demonstrates how seemingly benign configuration parameters can become attack vectors when not properly constrained against malicious input patterns.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could potentially expose sensitive system files, configuration data, and potentially even source code repositories that might be accessible through the traversal mechanism. Attackers could leverage this vulnerability to gain insights into the server's internal structure, access authentication credentials stored in configuration files, or discover other system components that might be vulnerable to additional attacks. The fact that this vulnerability affected all versions prior to specific security patches indicates a widespread exposure across the GitHub Enterprise Server user base, making it particularly concerning from a risk management perspective. Organizations using affected versions faced potential data breaches and system compromise risks that could impact their entire infrastructure.
Mitigation strategies for this vulnerability required immediate deployment of the security patches released in versions 3.1.3, 3.0.11, and 2.22.17, which implemented proper input validation and sanitization of user-controlled parameters in the GitHub Pages build process. System administrators should have conducted comprehensive security assessments of their GitHub Enterprise Server installations to identify any potential exploitation attempts and ensure proper patching across all affected instances. The vulnerability's discovery through the GitHub Bug Bounty program highlights the importance of coordinated disclosure and responsible vulnerability reporting mechanisms in identifying and addressing security flaws before they can be exploited in the wild. Organizations should also implement monitoring solutions to detect unusual GitHub Pages build activities that might indicate exploitation attempts, and consider implementing additional access controls and privilege restrictions for users who can create and build GitHub Pages sites to minimize the potential impact of similar vulnerabilities.