Connecting to a malicious Codespaces via GH CLI could allow command execution on the user's computer

The GitHub CLI version 2.6.1 and earlier are vulnerable to remote code execution through a malicious codespace SSH server when using `gh codespace ssh` or `gh codespace logs` commands. This has been patched in the cli v2.62.0.

Developers connect to remote codespaces through an SSH server running within the devcontainer, which is generally provided through the [default devcontainer image]( https://docs.github.com/en/codespaces/setting-up-your-project-for-codespaces/adding-a-dev-container-... https://docs.github.com/en/codespaces/setting-up-your-project-for-codespaces/adding-a-dev-container-configuration/introduction-to-dev-containers#using-the-default-dev-container-configuration) . GitHub CLI [retrieves SSH connection details]( https://github.com/cli/cli/blob/30066b0042d0c5928d959e288144300cb28196c9/internal/codespaces/rpc/inv... https://github.com/cli/cli/blob/30066b0042d0c5928d959e288144300cb28196c9/internal/codespaces/rpc/invoker.go#L230-L244 ), such as remote username, which is used in [executing `ssh` commands]( https://github.com/cli/cli/blob/e356c69a6f0125cfaac782c35acf77314f18908d/pkg/cmd/codespace/ssh.go#L2... https://github.com/cli/cli/blob/e356c69a6f0125cfaac782c35acf77314f18908d/pkg/cmd/codespace/ssh.go#L263 ) for `gh codespace ssh` or `gh codespace logs` commands.

This exploit occurs when a malicious third-party devcontainer contains a modified SSH server that injects `ssh` arguments within the SSH connection details. `gh codespace ssh` and `gh codespace logs` commands could execute arbitrary code on the user's workstation if the remote username contains something like `-oProxyCommand="echo hacked" #`. The `-oProxyCommand` flag causes `ssh` to execute the provided command while `#` shell comment causes any other `ssh` arguments to be ignored.

In `2.62.0`, the remote username information is being validated before being used.