Digital sign systems allowed hacker access through default passwords

Updated: A swathe of severe vulnerabilities was found in Tightrope Media Systems’ digital signage system.

A researcher has uncovered severe vulnerabilities in digital signage software developed by Tightrope Media Systems (TRMS) thanks to the use of a default password.

The findings were made due to a recent penetration test of the Carousel system conducted by cybersecurity researcher Drew Green.

Green's client was making use of the software on an appliance provided by TRMS which the researcher describes as "essentially an x86 Windows 10 PC."

As documented in a recent blog post, the tests began in the worst way -- as Green was able to walk straight in due to an unchanged default administrator password, a bug now assigned CVE-2018-18929.

After accessing the web interface without any need to guess or brute-force credentials, Green then found references online to an arbitrary file read (LFI) vulnerability present in the software's RenderingFetch API function, CVE-2018-14573.

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The researcher decided to explore further. TRMS's Carousel system allows users to upload "bulletins" which are the items displayed on digital signs.

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Drew Green

The interface accepts .ZIP files for uploads, and during testing, Green was not only able to export existing, legitimate bulletins, but was also able to upload a .ZIP file containing two malicious files to Carousel.

However, the researcher came across a stumbling block when he attempted to travel to the URL of the malicious files.

"It appeared that when inserting files into this ZIP archive, the path separator for files and directories was being set to the forward-slash character ("/") rather than the backslash character ("\")," Green said. "This caused the files I added to be discarded by the server upon upload. I was eventually able to see this clearly by opening the file in a hex editor."

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In order to overcome this barrier, all it took was for the researcher to manually change the characters in question. Green was then able to execute commands on the system via a web shell.

With access assured, the researcher uploaded a Powershell file which connected a remote shell back to his system -- granting Green the ability to upload arbitrary files and remotely execute code.

Another vulnerability, CVE-2018-18931, was uncovered which allowed the researcher to bump up privileges on a user account to a local administrator, and while exploiting the bug required a system restart -- something basic accounts cannot do -- he was able to send a command to force a reboot and trigger the exploit.

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The researcher notified Tightrope Media Systems of his findings in November 2018. The company responded by saying that the vulnerabilities were fixed in the latest version of the firm's signage software.

However, Green says that Tightrope Media Systems did not request the specifics of the bugs found.

"They have not followed-up with me to discuss with them the specifics of these vulnerabilities," Green says. "Now that approximately 90 days have elapsed since original disclosure, this information is being made publicly available."

Update 15.23 GMT: Tightrope Media Systems told ZDNet that the company is in the "process of notifying customers" and a patch release schedule to resolve the issues has been published.

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