Members of the Department of Government Efficiency uploaded a copy of a crucial Social Security database in June to a vulnerable cloud server, putting the personal information of hundreds of millions of Americans at risk of being leaked or hacked, according to a whistle-blower complaint filed by the Social Security Administration’s chief data officer.

The database contains records of all Social Security numbers issued by the federal government. It includes individuals’ full names, addresses and birth dates, among other details that could be used to steal their identities, making it one of the nation’s most sensitive repositories of personal information.

The account by the whistle-blower, Charles Borges, underscores concerns that have led to lawsuits seeking to block young software engineers at the agency built by Elon Musk from having access to confidential government data. In his complaint, Mr. Borges said DOGE members copied the data to an internal agency server that only DOGE could access, forgoing the type of “independent security monitoring” normally required under agency policy for such sensitive data and creating “enormous vulnerabilities.”

Mr. Borges did not indicate that the database had been breached or used inappropriately.

But his disclosure stated that as of late June, “no verified audit or oversight mechanisms” existed to monitor what DOGE was using the data for or whether it was being shared outside the agency. That kind of oversight would typically be provided by the agency’s career information security professionals, Mr. Borges said in his account.

And his complaint cites an official agency security assessment that described the project as “high risk” and that warned of “catastrophic impact” to Social Security beneficiaries and programs if the database were to be compromised.

“Should bad actors gain access to this cloud environment, Americans may be susceptible to widespread identity theft, may lose vital health care and food benefits, and the government may be responsible for reissuing every American a new Social Security number at great cost,” Mr. Borges’s complaint said. He alleged that DOGE did not involve him in discussions about the project, despite his role as chief data officer, leaving him to piece together evidence of what had happened after the fact.