CVE-2020-26233 in Git Credential Manager Core
Summary
by MITRE • 12/09/2020
Git Credential Manager Core (GCM Core) is a secure Git credential helper built on .NET Core that runs on Windows and macOS. In Git Credential Manager Core before version 2.0.289, when recursively cloning a Git repository on Windows with submodules, Git will first clone the top-level repository and then recursively clone all submodules by starting new Git processes from the top-level working directory. If a malicious git.exe executable is present in the top-level repository then this binary will be started by Git Credential Manager Core when attempting to read configuration, and not git.exe as found on the %PATH%. This only affects GCM Core on Windows, not macOS or Linux-based distributions. GCM Core version 2.0.289 contains the fix for this vulnerability, and is available from the project's GitHub releases page. GCM Core 2.0.289 is also bundled in the latest Git for Windows release; version 2.29.2(3). As a workaround, users should avoid recursively cloning untrusted repositories with the --recurse-submodules option.
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Analysis
by VulDB Data Team • 12/14/2020
The vulnerability described in CVE-2020-26233 represents a critical security flaw in Git Credential Manager Core versions prior to 2.0.289, specifically affecting Windows environments where the credential helper operates with elevated privileges during repository cloning operations. This issue stems from a path resolution weakness that allows for arbitrary code execution through manipulation of the Git executable within repository structures. The vulnerability is particularly concerning because it leverages the trust relationship between Git processes and their underlying credential management components, creating a potential attack vector for privilege escalation and credential theft.
The technical flaw manifests when Git Credential Manager Core processes recursive submodule cloning operations on Windows systems, where the helper attempts to read configuration data from the top-level repository directory. During this process, the system executes git.exe from the repository working directory rather than from the system PATH environment variable, creating an opportunity for malicious actors to place a compromised git.exe binary within the repository itself. This behavior violates the principle of least privilege and creates a scenario where legitimate Git operations can be hijacked to execute arbitrary code with the privileges of the user running the credential manager. The vulnerability maps directly to CWE-426 Untrusted Search Path, which specifically addresses the risks associated with executable search paths that do not properly validate the source of binaries.
The operational impact of this vulnerability extends beyond simple code execution, as it enables attackers to potentially compromise Git authentication credentials and access tokens that the credential manager handles. When recursively cloning repositories with submodules, the attacker-controlled git.exe binary can intercept or modify Git operations, potentially redirecting authentication requests to malicious endpoints or extracting sensitive information from the credential store. This threat is particularly severe in enterprise environments where Git repositories may contain proprietary code, confidential data, or access credentials for production systems. The vulnerability affects the broader Git ecosystem by undermining trust in repository cloning operations and potentially enabling supply chain attacks against development environments.
Mitigation strategies for this vulnerability require both immediate remediation and long-term operational changes to prevent exploitation. The primary fix involves upgrading to Git Credential Manager Core version 2.0.289 or later, which implements proper path resolution mechanisms to ensure that only trusted Git executables are executed during credential operations. Organizations should also implement defensive measures such as disabling recursive submodule cloning for untrusted repositories, implementing strict repository access controls, and monitoring for unauthorized modifications to repository structures. The workaround of avoiding --recurse-submodules option for untrusted repositories provides a temporary defense while systems are updated, though this approach may impact development workflows and collaborative development practices. This vulnerability highlights the importance of secure coding practices in credential management components and demonstrates how seemingly innocuous path resolution behaviors can create significant security risks in version control systems.
The security implications of this vulnerability align with ATT&CK technique T1552.001 Credential Access: Credentials In Files, as it enables attackers to potentially access stored Git credentials and authentication tokens through manipulated repository structures. Additionally, the flaw contributes to broader supply chain attack vectors by exploiting the trust relationships inherent in Git's recursive cloning behavior, where legitimate tools are used to execute malicious code within development environments. Organizations should consider implementing automated security scanning for Git repositories and credential manager configurations to detect and prevent exploitation of similar path resolution vulnerabilities in other tools and systems.