The padlock in your browser depends on a short list of trusted companies, called certificate authorities, vouching for websites. On Saturday, Oct 17, a security researcher told Google’s Chrome Root Program that private keys behind eight intermediate certificates from India-based certificate authority eMudhra were generated with too little randomness, per Google’s Chrome and Android security teams. That means anyone could work out the keys and forge a trusted HTTPS certificate to impersonate any website. Ars Technica reports the keys were absurdly small, and that the reporter proved it by publishing a message signed with one of them.
The good news. Chrome blocked the certificates within about two hours of the report, with no browser update or restart needed. Android devices got the same block through Google Play Services on Monday; restarting a phone pulls it immediately. Google says no certificates chaining to the affected certificates had shown up in public Certificate Transparency logs before the block, so Chrome couldn’t have been fooled by a forged one. Ars reports that by late Tuesday morning browser makers and some major apps and programming languages had blocked all eight, and there were no reports of the keys being used maliciously. The exception Ars found: Edge on Windows 10, which was still connecting to 12 vulnerable hosts when Ars published; Microsoft didn’t say whether a fix is coming.
The catch. Ars quotes Go cryptography maintainer Filippo Valsorda calling this “a massive cleanup job, bigger than Heartbleed,” because the fix also has to reach Linux servers, Docker containers, Internet-of-Things devices and tools that carry their own copy of trusted certificates. Linux distributions are still rolling out updates. Exploiting this takes an attacker sitting in the middle of your connection, which is hard on the open internet but much easier on a shared network like a coffee shop’s. Ars says VPNs are the most immediate concern. Signal, WhatsApp and WireGuard don’t rely on these certificates and aren’t affected.
Website owners and IT managers: find out whether any of your sites use a certificate that chains to emSign ECC Root CA - G3 (your certificate provider or web host can tell you). Google has removed that root from the Chrome Root Store, and the change reaches all devices relying on it the morning of Tuesday, Oct 27 (Pacific), sooner on Chrome Beta and Canary. After that, those sites will break in Chrome. Google says to get and install a new certificate from a different certificate authority now; eMudhra has committed to help affected customers move.
IT managers: apply your Linux distribution’s certificate updates as they ship, and check servers, containers, appliances and VPNs that don’t update themselves. If you use Edge on Windows 10, use Chrome or another updated browser until Microsoft confirms a fix.
At home: keep your browser and phone updated, and restart your Android phone if you haven’t lately. Be careful on public Wi-Fi until your devices are updated.