Officials have notified the vendor to confirm the issue and figure out a fix.
The Homeland Security Department is cautioning transportation operators about a security hole in some electronic freeway billboards that could let hackers display bogus warnings to drivers.
"The vulnerability is a hard-coded password that could allow unauthorized access to the highway sign," DHS officials said in an alert on Wednesday. [See update below.] Hard-coded passwords, sometimes called back doors, are default logins that software developers code into their programs. The vulnerability was identified in Daktronics Vanguard highway notification sign configuration software, officials said.
A "proof of concept" method to exploit the flaw has been made available, DHS officials warned. The Federal Highway Administration informed DHS of a public report of the vulnerability, Homeland Security officials said.
Officials have notified the vendor to confirm the issue and figure out a fix. In the meantime, they are recommending users "review sign messaging," update passwords and secure communication paths to the signs.
Daktronics freeway signs "convey clear, effective messages to high-speed traffic," according to the company's website, which features a photo of a North Carolina Department of Transportation sign in Asheville stating a road is closed due to a rock slide.
The DHS notice does not state whether all Daktronics highway signs or only certain models are vulnerable.
Daktronics officials declined to comment on whether their firm manufactured the signs that suffered breaches.
The company is working with DHS "to clarify the current alert and will release a statement once we have assessed the situation and developed customer recommendations," Daktronics spokeswoman Jody Huntimer said.
North Carolina officials also would not say whether their signs were made by Daktronics.
"We are continuing our investigation into the incident, and as such, respectfully decline to go into any details about that investigation," said David Ulmer, the chief information officer for the North Carolina Department of Transportation.
The hack in California involved a privately-owned sign that was being used to control traffic associated with an annual running event called Bay to Breakers, officials with the state of California said.
UPDATE: DHS late Thursday issued the following statement: "Daktronics reports that the password is not hardcoded as reported, but is a default password that can be changed upon installation."