CVE-2020-10519 in GitHub
Summary
by MITRE • 03/03/2021
A remote code execution vulnerability was identified in GitHub Enterprise Server that could be exploited when building a GitHub Pages site. User-controlled configuration of the underlying parsers used by GitHub Pages were not sufficiently restricted and made it possible to execute commands 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 2.22.7 and was fixed in 2.22.7, 2.21.15, and 2.20.24. The underlying issues contributing to this vulnerability were identified through the GitHub Security Bug Bounty program.
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Analysis
by VulDB Data Team • 03/14/2021
This remote code execution vulnerability in GitHub Enterprise Server represents a critical security flaw that emerged from improper input validation within the GitHub Pages site building process. The vulnerability stems from insufficient restrictions on user-controlled configuration of underlying parsers that GitHub Pages utilizes for site generation, creating a pathway for malicious command execution on the server instance. The flaw specifically impacts the parsing mechanism that processes user-supplied configuration files, allowing attackers to inject arbitrary commands that get executed within the context of the server environment. This type of vulnerability falls under the category of command injection as defined by CWE-77, where untrusted data is incorporated into system commands without proper sanitization or validation.
The exploitation scenario requires attackers to possess legitimate permissions to create and build GitHub Pages sites within the target Enterprise Server instance, making this vulnerability particularly concerning for organizations that grant extensive repository access or have compromised accounts. The attack vector leverages the trust placed in user-generated content during the site building process, where configuration files such as _config.yml or other parser configuration elements could contain malicious payloads. This vulnerability demonstrates the dangerous intersection of privilege escalation and code execution, as it allows an authenticated user to escalate their privileges beyond normal boundaries and execute arbitrary code on the underlying server infrastructure. The security implications extend beyond simple code execution to potentially enable full system compromise and lateral movement within the organization's infrastructure.
The impact of this vulnerability extends significantly beyond immediate code execution capabilities, as it can serve as a foothold for more sophisticated attacks within the enterprise environment. Organizations running affected versions of GitHub Enterprise Server face potential exposure to data breaches, system compromise, and unauthorized access to sensitive repositories and information. The vulnerability's presence in all versions prior to 2.22.7, 2.21.15, and 2.20.24 indicates a long-standing flaw that could have been exploited for extended periods. From an operational perspective, this vulnerability aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter and T1078.004 for Valid Accounts, as it requires legitimate user credentials but enables unauthorized code execution. The fix implemented in the patched versions demonstrates proper input validation and sanitization of user-supplied configuration parameters, effectively closing the command injection pathway. Organizations should prioritize immediate patching of affected systems, implement monitoring for suspicious repository activities, and review access controls to minimize potential exploitation opportunities.
The vulnerability's discovery through GitHub's Security Bug Bounty program highlights the importance of coordinated disclosure and community-driven security research in identifying and resolving critical flaws. This case study exemplifies how seemingly benign configuration parsing can become a critical security weakness when proper input validation is absent. The remediation approach taken by GitHub demonstrates the necessity of robust sanitization of user inputs and the implementation of principle of least privilege in configuration processing. Organizations should implement comprehensive security measures including regular vulnerability assessments, input validation controls, and privileged access management to prevent similar issues in their own systems. The vulnerability serves as a reminder that web applications must rigorously validate and sanitize all user-supplied data, particularly in contexts where that data influences system behavior or command execution.