Google blocked eight intermediate certificates issued by Indian certificate authority eMudhra after a researcher found their private keys could be recovered almost instantly, letting anyone forge certificates that browsers would accept for any website, Google's Chrome and Android security teams said Tuesday. Mozilla, Apple and Microsoft have taken similar steps. Chrome and Firefox are also removing the eMudhra root certificate above them, a step that will break some legitimate websites and leaves companies to check systems that browser fixes do not reach.
What Happened
A certificate authority vouches that a website is who it claims to be. It does so through a chain: a root certificate trusted by browsers and operating systems signs "intermediate" certificates, which in turn sign the certificates individual websites use. Whoever holds an intermediate's private key, the secret used to sign, can issue certificates that trusted software accepts.
According to Google's post, "Protecting Chrome and Android Users From Compromised eMudhra Intermediate CA Certificates," the Chrome Root Program received a researcher's report at 18:05 UTC Oct. 17 that keys for eight eMudhra intermediates had been generated with insufficient randomness. Chrome confirmed the finding and pushed a blocklist update at 19:45 UTC the same day, protecting users without a browser update. Android devices received an equivalent block through Google Play Services around 22:00 UTC Oct. 19.
Mozilla's incident report says six of the intermediates were for website certificates and two for code signing. Its preliminary analysis found the elliptic-curve private keys were integers smaller than 256, so they could be found by trying at most a few hundred values. Mozilla blocked the certificates through its OneCRL revocation list late Oct. 17 and shipped a Firefox update Oct. 20. Apple blocked them Oct. 19 and Microsoft Oct. 20, The Hacker News reported, and Sectigo, which had cross-signed some of the intermediates, revoked those cross-signed certificates, according to the Mozilla report.
In the Mozilla report, eMudhra gave a preliminary explanation: a flaw in a key-generation ceremony script in April 2025 created a second, weaker key pair, which was used by mistake because its label resembled the correct one. "There were human errors in multiple steps of the process," the company wrote. eMudhra revoked the intermediates Oct. 18, stopped issuing under the affected root and said it would re-verify every key ceremony it has performed. It also said the issuers were meant for its U.S. and European data centers and that only one went into production.
Why It Matters
A recoverable intermediate key is among the most serious failures in web encryption, because forged certificates let an attacker impersonate banks, email providers or internal portals without triggering warnings. Google said no website certificates chaining to the affected intermediates appeared in Certificate Transparency logs, the public records that Chrome requires certificates to appear in, before the block. That limits risk for Chrome users but not for every client.
BleepingComputer reported that software carrying its own certificate list or skipping revocation checks may keep trusting the certificates until patched. It cited macOS's built-in curl tool and listed Debian and Node.js updates as pending. For enterprises, that covers scripts, servers, appliances and applications well beyond the browser.
The root removal also creates an outage risk. eMudhra estimated in the Mozilla report that about 30,000 certificates need to move, most issued through automated tools, and said it is migrating customers to its RSA-based chain.
What to Watch
Google said its removal of emSign ECC Root CA - G3 should reach all devices relying on the Chrome Root Store on Oct. 27, and it urged site operators to get certificates from another trusted provider immediately. Google is also investigating whether eMudhra's other roots should remain trusted. Leaders should ask whether any vendor or internal system uses eMudhra certificates, and whether non-browser trust stores have been updated.
