Mozilla asks FBI for details on potential Firefox vulnerability used in Tor hack

Mozilla has asked a court that it should be provided information on a vulnerability in the Tor browser ahead of it being provided to a defendant in a lawsuit, as the browser is based in part on Firefox browser code.

“At this point, no one (including us) outside the government knows what vulnerability was exploited and whether it resides in any of our code base,” wrote Denelle Dixon-Thayer, chief legal and business officer at Mozilla, in a blog post Wednesday.

Mozilla is asking the U.S. District Court for the Western District of Washington in the interest of Firefox users to ensure that the government must disclose the vulnerability to it before it is revealed to any other party, as any disclosure without advance notice to Mozilla will increase the likelihood that the exploit will become public before Mozilla can fix any associated vulnerability in Firefox.

The Tor browser comprises a version of Firefox with some minor modifications that add privacy features, and the Tor proxy software that makes the browser’s Internet connections more anonymous, according to the filing.

The FBI had in 2015 used what it described as a “network investigative technique” to monitor users visiting a child pornography site, hidden on the so-called Tor anonymity network, which it had seized but kept live to identify its visitors.

The court has asked the government to produce information related to a security vulnerability that it exploited in the Tor browser. The defense wants information on the exploit to find out if the government exceeded its warrant conditions.

In its filing on Wednesday, Mozilla warned that “absent great care, the security of millions of individuals using Mozilla’s Firefox Internet browser could be put at risk by a premature disclosure of this vulnerability,” according to the filing.

The government has so far refused to tell Mozilla whether the vulnerability at issue in the case involves a Mozilla product. But Mozilla said in the filing that it has reason to believe that the exploit used by the government “is an active vulnerability in its Firefox code base that could be used to compromise users and systems running the browser.”

The government has also refused to tell Mozilla if the exploit went through the Vulnerabilities Equities Process (“VEP”), which is a government process for deciding whether to share or not information on security vulnerabilities, according to Mozilla.

If Mozilla is not allowed to intervene in the case to protect its interests, the court should certainly allow Mozilla to appear as a friend of the court or amicus curiae, according to the filing.