Chinese electronics giant TCL has acknowledged security holes in some models of its smart television sets, but denies that it maintains a secret “back door” that gives it control over deployed TVs.

In an email statement to The Security Ledger dated November 16, Senior Vice President for TCL North America Chris Larson acknowledged that the company issued a security patch on October 30 for one of two serious security holes reported by independent researchers on October 27. That hole, assigned the Common Vulnerabilities and Exposure (CVE) number 2020-27403 allowed unauthenticated users to browse the contents of a TCL smart TV’s operating system from an adjacent network or even the Internet.

A patch for a second flaw, CVE-2020-28055, will be released in the coming days, TCL said. That flaw allows a local unprivileged attacker to read from- and write to critical vendor resource directories within the TV’s Android file system, including the vendor upgrades folder.

The Security Ledger reported last week on the travails of the researchers who discovered the flaws, @sickcodes and @johnjhacking, who had difficulty contacting security experts within TCL and then found a patch silently applied without any warning from TCL.

A Learning Process for TCL

In an email statement to Security Ledger, Larson acknowledged that TCL, a global electronics giant with a market capitalization of $98 billion, “did not have a thorough and well-developed plan or strategy for reacting to issues” like those raised by the two researchers. “This was certainly a learning process for us,” he wrote.

At issue was both the security holes and the manner in which the company addressed them. In an interview with The Security Ledger, the researcher using the handle Sick Codes said that a TCL TV set he was monitoring was patched for the CVE-2020-27403 vulnerability without any notice from the company and no visible notification on the device itself.

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By TCL’s account, the patch was distributed via an Android Package (APK) update on October 30. APK files are a method of installing (or “side loading”) applications and code on Android-based systems outside of sanctioned application marketplaces like the Google Play store. The company did not address in its public statements the question of whether prior notification of the update was given to customers or whether TV set owners were required to approve the update before it was installed.

Limited Impact in North America

However, the patch issued on October 30 is unlikely to have affected TCL customers in the U.S. and Canada, as none of the TCL models sold in the North America contain the CVE-2020-24703 vulnerability, TCL said in its statement. However, some TCL TV models sold in the U.S. and Canada are impacted by CVE-2020-28055, the company warned. They are TCL models 32S330, 40S330, 43S434, 50S434, 55S434, 65S434, and 75S434.

The patched vulnerability was linked to a feature called “Magic Connect” and an Android APK by the name of T-Cast, which allows users to “stream user content from a mobile device.” T-Cast was never installed on televisions distributed in the USA or Canada, TCL said. For TCL smart TV sets outside of North America that did contain T-Cast, the APK was “updated to resolve this issue,” the company said. That application update may explain why the TCL TV set studied by the researchers suddenly stopped exhibiting the vulnerability.

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No Back Doors, Just “Remote Maintenance”

While TCL denied having a back door into its smart TVs, the company did acknowledge the existence of remote “maintenance” features that could give its employees or others control over deployed television sets, including onboard cameras and microphones.

In particular, TCL acknowledges that an Android APK known as “Terminal Manager…supports remote diagnostics in select regions,” but not in North America. In regions where sets with the Terminal Manager APK are deployed, TCL is able to “operate most functions of the television remotely.” That appears to include cameras and microphones installed on the set.

However, TCL said that Terminal Manager can only be used if the user “requests such action during the diagnostic session.” The process must be “initiated by the user and a code provided to TCL customer service agents in order to have diagnostic access to the television,” according to the company’s FAQ.

Other clarifications from the vendor suggest that, while reports of secret back doors in smart TVs may be overwrought, there is plenty of reason to worry about the security of TCL smart TVs.

The TCL statement acknowledged, for example, that two publicly browsable directories on the TCL Android TVs identified by the researchers could have potentially opened the door for malicious actors. A remotely writeable “upgrade” directory /data/vendor/upgrade on TCL sets has “never been used” but is intended for over the air firmware upgrades. Firmware update files placed in the directory are loaded on the next TV reboot. Similarly a directory /data/vendor/tcl, has also “never been used,” but stores “advertising graphics” that also are loaded “as part of the boot up process,” TCL said.

Promises to work with Independent Researchers

The company said it has learned from its mistakes and that it is undertaking efforts to work more closely with third party and independent security researchers in the future.

“Going forward, we are putting processes in place to better react to discoveries by 3rd parties. These real-world experts are sometimes able to find vulnerabilities that are missed by testing. We are performing additional training for our customer service agents on escalation procedures on these issues as well as establishing a direct reporting system online,” the company said.

China Risk Rising

Vendor assurances aside, there is growing concern within the United States and other nations about the threat posed by hundreds of millions of consumer electronic devices manufactured – or sourced in China. The firm Intsights in August warned that China was using technological exports as “weaponized trojans in foreign countries.” The country is “exporting technology around the world that has hidden backdoors, superior surveillance capability, and covert data collection capabilities that surpass their intended purposes and are being used for widespread reconnaissance, espionage, and data theft,” the company warned, citing reports about gear from the telecommunications vendor Huawei and social media site TikTok among others.

Western governments and non-governmental organizations have also raised alarms about the country’s blend of technology-enabled authoritarianism, including the use of data theft and data harvesting, coupled with artificial intelligence to identify individuals whose words or actions are counter to the ruling Communist Party.

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