Security Experts:

TLS Bug in Blue Coat Proxy Breaks Chromebooks, PCs

Products from Symantec-owned Blue Coat and likely other vendors can cause serious problems for devices running the Chrome web browser or Chrome OS due to poor implementation of the TLS 1.3 protocol.

Google warned last week that the use of Blue Coat proxies causes connection problems when Chrome 56 or Chrome OS 56 attempt to connect via TLS 1.3. The tech giant believes the issue affects products running version 6.5 of the Blue Coat SGOS operating system.

An employee of Montgomery County Public Schools in Maryland reported that thousands of the organization’s Chromebooks and PCs had broken down due to the bug. The affected devices had automatically updated to Chrome OS 56, respectively Chrome 56, which introduce support for TLS 1.3.

The employee said the organization’s Chromebooks are “stuck in a state of flickering between a login screen and a ‘Network not available’ screen. Occasionally, you can see a SSL_HANDSHAKE_ERROR briefly at the login screen before switching back to the ‘Network not available’ screen.”

Other major education organizations are affected as well, likely because SSL/TLS inspection is common in this sector, Google said.

The company has provided some workarounds and released a Chrome update that disables TLS 1.3. A future version of the web browser will re-enabled TLS 1.3; hopefully, firewall and proxy vendors will address the issue until then.

According to Google, Blue Coat was informed about the introduction of TLS 1.3 support several months ago, but the company failed to properly test its software. SecurityWeek has reached out to Symantec for comment and will update this article if the company responds.

A study conducted recently by researchers from Mozilla, Google, CloudFlare and various universities showed that many antiviruses and network appliances that intercept TLS connections for visibility into encrypted traffic weaken security and introduce vulnerabilities.

The study found that only Blue Coat’s ProxySG product maintained an optimal TLS connection, but those tests were conducted on TLS 1.2.

TLS 1.3 is still under development, but a final version is expected soon. The new version of the protocol improves speed and eliminates some of the features that have been leveraged in the TLS attacks disclosed over the past years.

Related: Blue Coat Fixes Several Flaws in SSL Visibility Appliance

Related: CloudFlare Adds Support for TLS 1.3

Related: OpenSSL Patches TLS Flaw Exposing Many HTTPS Servers

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.