Weak eMudhra Keys Enable Thousands of Rogue Certificates

Eight intermediate certificates issued by Indian certificate authority eMudhra were found to rely on trivially weak private keys, creating a severe cryptographic risk. The EM OV TLS CA – G3C intermediate certificate used a private key consisting solely of the integer 4, meaning that anyone with the corresponding public key could forge legitimate subordinate certificates for any domain.

The article attributes these findings to a security researcher and notes that the issue prompted broad industry alarm as the weak keys affected multiple trust chains.

In response, modern browsers and operating systems revoked the compromised certificates, with desktop browsers rejecting connections that chain to the affected authorities. However, legacy systems and many IoT devices may not properly check Certificate Revocation Lists or update root stores promptly, leaving some users exposed where the intermediate certificate remains trusted.

Public Certificate Transparency monitors subsequently logged a large volume of forged records, including over 106,000 unauthorized certificates for google[.]com, and more than 107,000 rogue issuances in a matter of hours, the vast majority (about 99 per cent) aimed at Google domains.

The article explains that CT logs record certificates independently of whether the issuing CA validated domain control, and that RFC 9162 permits submission of signed certificates with attached trust chains to public monitors, which allowed the forged eMudhra certificates to appear in the records.

The report cites Mozilla’s Bugzilla incident report on eMudhra weak keys (Bug 2083449) as documentation of the event's testing and monitoring activity.