Summary of the Private Key Compromise of an eMudhra Intermediate CA Certificate - piyolog

What happened

On October 17, 2026, researchers reported that the private keys of 8 intermediate CA certificates from eMudhra were exposed. Anyone could work out these keys from the public keys. Browsers blocked the affected CAs the same day. eMudhra revoked all 8 on October 18. Mozilla then removed the root certificate above the TLS intermediates from its trust list.

Key numbers and facts

• 8 intermediate CA certificates were affected: 6 for TLS (website security) and 2 for code signing.
• Sectigo also cross-signed these 8, so the same keys have 16 certificates in total.
• eMudhra says it issued no end-entity certificates from these 8 CAs, and only 1 was used in production.
• The key ceremony was held on April 30, 2025, where eMudhra created 24 intermediate CAs.
• Mozilla says the keys were weak: they were integers below 256 and could be recovered almost instantly.

Why the keys were weak

A key ceremony is a planned, recorded event where new CA keys are created inside a secure device called an HSM. In this case, eMudhra says a test of key wrapping (a way to export keys) was approved as a deviation. A bug then created a second, weak key pair inside the HSM. Because the labels of the keys looked similar, the weak key was used by mistake to make a certificate request, and the root CA signed it. eMudhra also had a similar problem in 2025, when a certificate revocation list (CRL) was signed with the wrong key.

Why it matters

Anyone holding the 6 TLS keys could create a TLS certificate for any domain. An attacker who can intercept traffic could use such a certificate to pretend to be a real website and read or change encrypted data. This only works while browsers and other clients trust these certificate chains. eMudhra says there was no break-in and no data leak. The code signing keys could be used to make fake code signing certificates, so malware might look like it came from a trusted publisher. Checks so far show no known abuse.

What to watch

• Whether eMudhra publishes the full root cause report, which it promised after its investigation.
• Changes to eMudhra's key ceremony process, which it says it is reviewing completely.
• Sites that use the removed root must move to a certificate from another chain. Some non-Firefox servers may stop working until they do.
• Chrome Root Store version 43, which will remove the root and reach devices from October 27, 2026.
• Whether Chrome's question to eMudhra about the 2025 CRL signing problem gets a clear answer.