As long as they act they will be fine. Github will be more at risk, since they are legally responsible for content hosted on their site. They have some protections under the DMCA, but only if they respond to takedown requests in a timely manner. And those takedown requests take time and effort to process.
The RIAA and other copyright holder representatives have automated submitting a DMCA takedown request process ages ago, and now submit thousands a day to e.g. youtube. Youtube in turn has automated taking down content that receives said requests and probably a big part of the appeal process as well. Is Github that far already?