Mozilla Warns of SHA-1 Deprecation Side Effects

Mozilla warns Firefox users that the browser’s rejection of new SHA-1 certificates is keeping some users behind security scanners and antivirus software from reaching HTTPS sites.

As promised, Mozilla officially began rejecting new SHA-1 certificates as of the first of the year. And as promised, there have been some usability issues.

Mozilla yesterday said that some security scanners and antivirus products are keeping some from reaching HTTPS websites.

“When a user tries to connect to an HTTPS site, the man-in-the-middle device sends Firefox a new SHA-1 certificate instead of the server’s real certificate,” said Richard Barnes of Mozilla. “Since Firefox rejects new SHA-1 certificates, it can’t connect to the server.”

A number of experts voiced their concerns late last year as most of the major browsers inched toward self-imposed deadlines for rejecting SHA-1 certificates that significant portions of the Internet would be cut off.

Facebook chief security officer Alex Stamos put the number at tens of millions, while CloudFlare CEO Matthew Prince was more specific saying that as many as 37 million would be stranded.

“A disproportionate number of those people reside in developing countries, and the likely outcome in those counties will be a serious backslide in the deployment of HTTPS by governments, companies and NGOs that wish to reach their target populations,” Stamos said.

Prince added that circumstances are different today regarding support for newer crypto algorithms. Unlike when MD5 was put out to pasture and SHA-1 support was widespread, the same cannot be said for SHA-2, which is also not supported on older mobile devices.

“In a Silicon Valley tech company, where most employees get a new laptop every year and having a 5-year-old phone is unheard of, this may not seem like a problem. But the Internet is used by billions of people around the world and most of them don’t have the latest technology,” Prince said.

SHA-1 is considered theoretically broken, and academics say that given the resources and computing power, practical collision attacks are well within reach of nation-state attackers, for example.

Barnes said there are workarounds short of manually installing the latest version of Firefox, since updates are provided over HTTPS.

“If you want to avoid reinstalling, advanced users can fix their local copy of Firefox by going to about:config and changing the value of “security.pki.sha1_enforcement_level” to 0 (which will accept all SHA-1 certificates),” Barnes said.

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