CVE-2024-56731: Gogs deletion of internal files allows 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

diff + // 🚨 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 RUNUSER in the configuration. It allows attackers to access and alter any users' code hosted on the same instance.