CVE-2016-3068 in Mercurial
Summary
by MITRE
Mercurial before 3.7.3 allows remote attackers to execute arbitrary code via a crafted git ext:: URL when cloning a subrepository.
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Analysis
by VulDB Data Team • 07/24/2022
The vulnerability identified as CVE-2016-3068 represents a critical remote code execution flaw in Mercurial version 3.7.2 and earlier, specifically affecting the handling of git ext:: URLs during subrepository cloning operations. This vulnerability resides in the Mercurial distributed version control system's implementation of subrepository functionality, where the software fails to properly sanitize user-provided URLs before executing them as shell commands. The flaw enables attackers to craft malicious git ext:: URLs that, when processed during subrepository cloning, can trigger arbitrary command execution on the victim system. This represents a classic command injection vulnerability that leverages the trust placed in repository metadata during the cloning process.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within Mercurial's subrepository handling code. When Mercurial encounters a subrepository definition containing a git ext:: URL, it attempts to execute the URL as a shell command without adequate sanitization of the URL components. The git ext:: protocol allows specifying custom command execution through the use of the git protocol with remote command execution capabilities. Attackers can manipulate the URL to include shell metacharacters and commands that will be executed with the privileges of the user running the Mercurial process. This vulnerability operates at the intersection of command injection and remote code execution, with the potential for full system compromise depending on the execution context and privileges of the Mercurial process.
The operational impact of CVE-2016-3068 is severe and far-reaching, as it allows remote attackers to execute arbitrary code on systems that clone repositories containing malicious subrepository definitions. This vulnerability affects any system running Mercurial 3.7.2 or earlier versions that processes untrusted repository data, particularly in environments where developers clone repositories from untrusted sources or when automated systems handle repository cloning operations. The attack surface expands significantly in continuous integration environments, development servers, and any system where automated repository cloning occurs. An attacker who can influence a repository's subrepository definition can potentially execute commands such as downloading malware, establishing reverse shells, or modifying system files. This vulnerability directly maps to CWE-78, which describes improper neutralization of special elements used in OS commands, and aligns with ATT&CK technique T1059.007 for executing commands through a shell, representing a significant threat to software development environments and CI/CD pipelines.
The mitigation strategy for CVE-2016-3068 centers on upgrading to Mercurial version 3.7.3 or later, where the vulnerability has been addressed through proper input validation and sanitization of git ext:: URLs. Organizations should implement immediate patch management procedures to update all affected systems and verify that the upgrade has been successfully applied. Additionally, administrators should consider implementing network-level restrictions that prevent access to potentially malicious repositories, particularly those from untrusted sources. The vulnerability can be mitigated through careful repository access controls and ensuring that subrepository definitions are validated before cloning operations. Security teams should also monitor for any unauthorized repository modifications or attempts to inject malicious subrepository configurations into development environments. Implementing automated security scanning tools that can detect malicious subrepository definitions and establishing secure coding practices for repository management can further reduce the risk exposure associated with this vulnerability.