CVE-2022-39253: Git Information Disclosure Vulnerability

CVE-2022-39253 Overview

CVE-2022-39253 is a sensitive information exposure vulnerability affecting Git, the widely-used open source distributed revision control system. This vulnerability allows a malicious actor to expose sensitive information from a victim's machine through a symbolic link attack during local clone operations. When performing a local clone (where the source and target of the clone are on the same volume), Git copies the contents of the source's $GIT_DIR/objects directory into the destination by either creating hardlinks to the source contents, or copying them if hardlinks are disabled via --no-hardlinks.

A malicious actor could convince a victim to clone a repository containing a symbolic link pointing at sensitive information on the victim's machine. The attack can be executed either by having the victim clone a malicious repository on the same machine, or by having them clone a malicious repository embedded as a bare repository via a submodule from any source when using the --recurse-submodules option.

Critical Impact

Successful exploitation allows attackers to read arbitrary files from the victim's machine, potentially exposing SSH keys, credentials, configuration files, and other sensitive data through crafted symbolic links in malicious Git repositories.

Affected Products

• Git versions prior to 2.30.6, 2.31.5, 2.32.4, 2.33.5, 2.34.5, 2.35.5, 2.36.3, and 2.37.4
• Apple Xcode (prior to patched version)
• Fedora 35, 36, and 37
• Debian Linux 10.0

Discovery Timeline

• 2022-10-18 - Security patches released for affected Git versions
• 2022-10-19 - CVE-2022-39253 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-39253

Vulnerability Analysis

This vulnerability stems from improper handling of symbolic links during Git's local clone optimization process. When a user clones a repository locally, Git attempts to optimize the operation by creating hardlinks to objects in the source repository's $GIT_DIR/objects directory. While Git does not normally create symbolic links in this directory, the vulnerability allows a malicious repository to contain symbolic links that, when cloned, can be followed to read sensitive files outside the repository context.

The attack surface is particularly concerning in environments where users may clone repositories from untrusted sources on shared machines or when using the --recurse-submodules option. The submodule attack vector is especially dangerous because a malicious bare repository can be embedded as a submodule in an otherwise legitimate-looking repository from any hosting source.

The vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) and CWE-59 (Improper Link Resolution Before File Access), indicating both the information disclosure impact and the root cause being improper symlink handling.

Root Cause

The root cause lies in Git's local clone functionality failing to properly validate or restrict symbolic links within repository contents during the clone operation. Git's design assumes the $GIT_DIR/objects directory will not contain symbolic links, but this assumption does not account for maliciously crafted repositories that exploit the local clone optimization to follow symbolic links and expose arbitrary file contents from the victim's system.

Attack Vector

The attack requires local access in the sense that the victim must perform a clone operation on their machine. The attacker must craft a malicious repository containing symbolic links pointing to sensitive files on the target system (such as ~/.ssh/id_rsa, /etc/passwd, or application configuration files). The victim is then socially engineered into cloning this repository using one of two methods:

1. Direct local clone: The victim clones the malicious repository located on a shared machine or network volume using Git's local optimization
2. Submodule attack: The victim clones any repository that contains the malicious repository embedded as a bare repository submodule while using the --recurse-submodules flag

Upon successful exploitation, the attacker gains access to the contents of files that the symbolic links pointed to, leading to potential exposure of credentials, private keys, and other sensitive data.

Detection Methods for CVE-2022-39253

Indicators of Compromise

• Unusual symbolic links present in cloned repository directories pointing to sensitive system paths
• Repository objects containing references to files outside the normal repository structure (e.g., ~/.ssh/, /etc/, user home directories)
• Unexpected file access events to sensitive files like SSH keys or credential files during or after Git clone operations
• Presence of bare repositories embedded as submodules with suspicious symbolic link patterns

Detection Strategies

• Monitor Git clone operations for access to files outside the expected repository scope, particularly sensitive paths like ~/.ssh/ or /etc/
• Implement file integrity monitoring on critical files to detect unexpected read access during Git operations
• Use endpoint detection solutions to correlate Git process activity with sensitive file access patterns
• Audit submodule configurations in repositories for embedded bare repositories from untrusted sources

Monitoring Recommendations

• Configure logging for Git operations to capture clone commands and associated file system activities
• Deploy SentinelOne's endpoint protection to detect anomalous file access patterns associated with Git processes
• Implement alerts for any Git clone operations using the --recurse-submodules flag on shared or multi-user systems
• Monitor for new or modified symbolic links in repository directories that point to system paths outside the repository

How to Mitigate CVE-2022-39253

Immediate Actions Required

• Upgrade Git to patched versions: 2.30.6, 2.31.5, 2.32.4, 2.33.5, 2.34.5, 2.35.5, 2.36.3, 2.37.4, or later
• Avoid cloning repositories from untrusted sources on shared machines until patched
• When cloning untrusted repositories, use the --no-local option or clone from URLs using the file:// scheme to bypass the local optimization
• Avoid using --recurse-submodules when cloning repositories from untrusted sources

Patch Information

The Git maintainers released patches on 2022-10-18 addressing this vulnerability across multiple version branches. The fix prevents symbolic links from being followed during local clone operations. Updates are available through the official Git distribution and package managers for major Linux distributions including Fedora and Debian. Apple has addressed this issue in Xcode updates as documented in Apple Support Article HT213496. For detailed information, see the GitHub Security Advisory GHSA-3wp6-j8xr-qw85.

Workarounds

• Use --no-local flag when cloning repositories to prevent Git from using the local optimization that is vulnerable to this attack
• Clone repositories using the file:// scheme URL format instead of direct paths to avoid the local clone optimization
• Configure Git globally to restrict file protocol access with git config --global protocol.file.allow user
• Avoid using --recurse-submodules when cloning repositories from untrusted sources until systems are patched
• On shared machines, ensure users only clone repositories from trusted sources

# Configuration example
# Disable local optimization when cloning untrusted repositories
git clone --no-local /path/to/potentially/untrusted/repo

# Or clone using file:// scheme to avoid local optimization
git clone file:///path/to/repository

# Configure global protocol restrictions
git config --global protocol.file.allow user

# Clone without recursive submodules from untrusted sources
git clone --no-recurse-submodules https://example.com/repo.git