CVE-2021-29468 in Cygwin Git
Summary
by MITRE • 04/30/2021
Cygwin Git is a patch set for the git command line tool for the cygwin environment. A specially crafted repository that contains symbolic links as well as files with backslash characters in the file name may cause just-checked out code to be executed while checking out a repository using Git on Cygwin. The problem will be patched in the Cygwin Git v2.31.1-2 release. At time of writing, the vulnerability is present in the upstream Git source code; any Cygwin user who compiles Git for themselves from upstream sources should manually apply a patch to mitigate the vulnerability. As mitigation users should not clone or pull from repositories from untrusted sources. CVE-2019-1354 was an equivalent vulnerability in Git for Visual Studio.
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Analysis
by VulDB Data Team • 05/03/2021
The vulnerability identified as CVE-2021-29468 represents a critical security flaw in Cygwin Git that enables arbitrary code execution during repository checkout operations. This issue specifically affects the git command line tool when running within the Cygwin environment, creating a dangerous scenario where maliciously crafted repositories can trigger unintended execution of code. The vulnerability stems from how Git handles symbolic links and file names containing backslash characters during the checkout process, allowing attackers to exploit the parsing logic in ways that were not properly secured against malicious input. The flaw exists at the intersection of Cygwin's POSIX compatibility layer and Git's repository handling mechanisms, creating a pathway for privilege escalation through seemingly benign repository operations.
The technical implementation of this vulnerability involves a specific parsing sequence where Git's checkout routine encounters symbolic links combined with file names containing backslash characters. When these elements are processed together, the parsing logic incorrectly interprets the backslash characters as path separators or escape sequences, leading to unexpected behavior in the file system operations. This misinterpretation allows the system to execute code from files that are part of the repository structure rather than simply creating or modifying files as intended. The vulnerability manifests specifically during the checkout phase when Git attempts to resolve symbolic links and process file names, creating an execution flow that bypasses normal security controls. This behavior aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and represents a variant of path traversal vulnerabilities that exploit how different operating systems handle path resolution.
The operational impact of CVE-2021-29468 is severe and far-reaching for Cygwin users who regularly work with Git repositories. Any user who checks out repositories from untrusted sources could unknowingly execute malicious code on their system, potentially leading to complete system compromise. The vulnerability affects not just individual developers but also organizations that rely on Git for version control and collaborative development, as it can be exploited through supply chain attacks where malicious repositories are introduced into development workflows. The risk is particularly high in environments where developers frequently pull code from external sources or collaborate on projects hosted on public repositories. The vulnerability's presence in upstream Git source code means that users who compile Git from source without applying the appropriate patches are exposed, creating a broader attack surface than initially apparent. This situation mirrors the patterns seen in CVE-2019-1354, which affected Git for Visual Studio, indicating that similar issues can emerge across different Git implementations and environments.
Mitigation strategies for CVE-2021-29468 require immediate action from affected users and organizations. The primary recommendation is to upgrade to Cygwin Git version 2.31.1-2 or later, which contains the official patch for this vulnerability. Users who compile Git from upstream sources must manually apply the specific patch that addresses the symbolic link and backslash parsing issue. The most effective immediate mitigation is to avoid cloning or pulling repositories from untrusted sources, as this prevents exposure to maliciously crafted repositories that could exploit the vulnerability. Organizations should implement repository scanning and validation processes before integrating external code into their development workflows. Additionally, system administrators should consider implementing network-level controls to restrict access to potentially malicious repositories and establish secure coding practices for Git operations. The vulnerability demonstrates the importance of proper input validation and secure parsing of file system operations, particularly in cross-platform environments where different operating system behaviors can create unexpected security implications. Security teams should also monitor for similar patterns in other Git implementations and ensure that their patch management processes account for vulnerabilities that may affect multiple Git variants across different platforms.