Company Accidentally Allowed Contractor To Work On Contract W/o Proper Authorization

My brother is employed by a company that provides contractor support to government agencies. Fall 2024 he unfortunately had some financial troubles due to the change in his family income when his wife unexpectedly went into the hospital with severe medical issues and an accidental missed payment ended up reflecting on his credit report. He had to address this and provide an explanation to his employer, and somewhere during the process he unknowingly missed a step. He was under the impression all was good as he hadn't heard anything else after submitting what he believed was everything to his employer.

Well this past week he received a call from his supervisor who informed him that they had to immediately remove him from the government contract he was working on as they just became aware his clearance had been revoked back in October due to him missing a necessary step. This unfortunately means he had been working on this contract for 4 months without the proper clearance to do so. This obviously would violate their contract with the government & would be grounds for it to be terminated as well as potential fines & penalties charged to the company. For now, he's been requested not to mention or discuss the issue with anyone and to not respond to any contact attempts from the people he worked with on the contract as they work with their legal team to identify the course of action for the company to take.

He has no idea what the possible courses of action for this situation could be, or how each would potentially affect him. I'm sure it's very possible depending on how they decide to try to handle the situation that they may attempt to have him sign an NDA. He obviously had no way of knowing his clearance was no longer active as it would have been his employers responsibility to monitor the status & notify him of any issues. Is it possible he will need consider consulting a lawyer to protect himself?