eMudhra CA Keys Compromised: One Private Key Was the Number 4

Eight eMudhra intermediate certificates had private keys so weak anyone could guess them. Mozilla blocked them in Firefox within 3 hours. Here's what that means for HTTPS and what you should update.

Wassap mga BitLods.

Imagine your house key is supposed to be a 116-digit secret number.

And yours is... 4.

That's basically what happened to eMudhra, an Indian certificate authority (CA), this week. And because CAs are the reason your browser trusts that padlock icon, this one matters to everybody, not just security nerds.

What happened

On 17 October 2026, Mozilla got a report that the private keys of eight eMudhra intermediate certificates were compromised.

These intermediates use P-384 keys. A proper P-384 private key is a random number around 116 digits long. The eMudhra ones weren't. Researchers recovered all eight keys from their public certificates in under a second, and every single one was smaller than 256:

4, 56, 66, 115, 155, 156, 230, 237

The one that was literally 4 belonged to the intermediate called EM OV TLS CA - G3C. Mozilla's own summary says the key generation process "was flawed and is trivial to exploit."

Why that's scary

A CA's private key is what it uses to sign HTTPS certificates. If you have the key, you can sign a certificate for any website: your bank, Gmail, Facebook, cebkun.com, anything.

So with these keys, an attacker who can sit between you and the internet (shady public Wi-Fi, a compromised router, a hostile network) could show you a fake site with a valid-looking padlock. Walang red warning. Mukhang legit.

Two of the eight were code signing intermediates too, which means the same trick could be used to make malware look "signed."

There's no public evidence these keys were used to attack anyone. But since anyone could figure them out, you have to assume they could have been.

How it happened

According to eMudhra's preliminary explanation (as reported by Help Net Security), a faulty script at their April 2025 key ceremony created a second set of weak keys in the hardware security module. Those had names similar to the real ones and got used by mistake. Sectigo had also cross-signed the intermediates.

That's eMudhra's account, and independent checks are still going. eMudhra says its root keys and other intermediates are fine.

What browsers did

This is the good part:

Mozilla blocked the eight certificates in Firefox through OneCRL (its revocation list) in less than 3 hours after the report, for Firefox users with standard settings.
Mozilla also removed the eMudhra root that signed them from NSS, the trust store many other apps use.
Chrome blocked them too, with Apple and Microsoft following within a few days, based on news reports.
eMudhra revoked the intermediates on 18 October, and Sectigo revoked its cross-signed copies a day later.

Who's still at risk

Updated browsers are likely fine. The risk is everything that doesn't check revocation lists:

Old phones and tablets that stopped getting updates.
Smart TVs, IoT gadgets, routers.
Apps and scripts with their own bundled certificate list (older Node, Python certifi, Java, Docker images built months ago).

These keep trusting whatever was in their certificate store when they were built, until someone updates them.

What to do

Regular users:

Update your browser (Firefox, Chrome, Edge, Safari) and restart it.
Update your phone and laptop OS.
Be extra careful on public Wi-Fi until you've updated.

Devs and site owners:

Update OS CA bundles (ca-certificates on Linux) and rebuild Docker images so they pick up the change.
Update language trust stores like Python's certifi and your Java cacerts.
If your own site uses an eMudhra certificate, contact them and move to a certificate from a different chain. Browsers may stop trusting that root.

The BitLods takeaway

The whole HTTPS system runs on trust in a few hundred CAs. When one messes up, browsers have to move fast, and this time they did.

Your job is the boring part: update your stuff. Browser, OS, containers, old devices. Boring saves lives.

Sources

Details are still coming out, especially eMudhra's final incident report. Follow the official sources above for updates.