CVE-2024-56731: Gogs allows deletion of internal files which leads to remote command execution

Summary

Due to the insufficient patch for the CVE-2024-39931, it's still possible to delete files under the .git directory and achieve remote command execution.

Details

In the patch for CVE-2024-39931, the following check is added: https://github.com/gogs/gogs/commit/77a4a945ae9a87f77e392e9066b560edb71b5de9

+	// 🚨 SECURITY: Prevent uploading files into the ".git" directory
+	if isRepositoryGitPath(opts.TreePath) {
+		return errors.Errorf("bad tree path %q", opts.TreePath)
+	}

While the above code snippet checks if the specified path is a .git directory, there are no checks for symbolic links in the later steps. So, by creating a symbolic link that points to the .git directory, an attacker can still delete arbitrary files in the .git directory and achieve remote command execution.

Impact

Unprivileged user accounts can execute arbitrary commands on the Gogs instance with the privileges of the account specified by RUN_USER in the configuration. It allows attackers to access and alter any users' code hosted on the same instance.