Pierluigi Paganini May 05, 2019

Tor users noticed that the NoScript and HTTPS-Everywhere add-ons were disabled in the Tor browser, what’s happened?

A few days ago millions of users discovered that Mozilla Add-ons were disabled and they were not able to re-activate or re-install them.

The issue was caused by an expired intermediary certificate used to digitally sign Mozilla add-ons.

The problem also affected the Firefox browser bundled with Tor. Tor users observed the NoScript and HTTPS-Everywhere add-ons were disabled in the Tor browser.

“Due to a mistake in Mozilla’s signing infrastructure, NoScript and all other Firefox extensions signed by Mozilla have been disabled in Tor Browser. Because they use NoScript, higher security levels are currently broken for Tor Browser users.” reads the post published by the Tor Project.

“Mozilla is working on a fix, and we’ll start building a new Tor Browser version as soon as their fix is available.”

Starting on Friday I received many messages from my friends that were observing the strange behavior. The users that were attempting to launch Tor were displayed the following message

“One or more installed add-ons cannot be verified and have been disabled.”

Both the NoScript and HTTPS-Everywhere add-ons were disabled because they “could not be verified for use in Tor browser”.

Experts at the Tor Project provided this temporary fix that could address the issue until Tor will release a new version to address the problem.

“Meanwhile, anyone who is dependent on the security provided by the higher security levels can apply the following workaround:

• Open the address about:config in the Tor Browser address bar
• At the top of the page, search for xpinstall.signatures.required
• Set the xpinstall.signatures.requiredentry to false by double clicking it

Experts pointed out that the above workaround should only be used as a temporary solution because it disables a security feature. Tor users must set the xpinstall.signatures.required entry back to true again once the Tor Browser security update is applied.

To disabled signatures, go to about:config and search for xpinstall.signatures.required. Right-click on the entry and select Toggle. 

Once completed the temporary fix, Tor users will see the following message:

“NoScript could not be verified for use in Tor Bowser. Proceed with caution.”

Pierluigi Paganini

(SecurityAffairs – Tor Browser, NoScript)

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