Browsers Block eMudhra Intermediate CAs Over Recoverable Private Keys

In April 2025, eMudhra issued eight intermediate certificates whose private keys were compromised due to insufficient randomness in key generation. The weak keys were effectively all-zeroes except for the last byte and could be recovered quickly using the baby-step giant-step discrete log algorithm. This vulnerability enables attackers to forge trusted HTTPS certificates to impersonate any website for clients still trusting these intermediates. Major browsers (Mozilla Firefox, Google Chrome, Apple Safari, Microsoft Edge) blocked these certificates between October 17 and October 20, 2026. eMudhra revoked the certificates and is investigating code and process flaws in their key lifecycle management. Although no evidence of malicious use was found in Certificate Transparency logs, some clients may still trust the compromised certificates until updated.

Attackers with access to the compromised private keys could generate fraudulent TLS certificates trusted by affected clients, enabling impersonation of any website. This undermines the trust model of HTTPS and could facilitate man-in-the-middle attacks against users trusting these intermediates. While major browsers and trust stores have blocked and revoked the certificates, clients that have not updated their trust stores remain vulnerable. No confirmed malicious use has been observed in public logs, but the risk remains until all clients remove trust in the compromised intermediates.

The compromised certificates have been revoked and blocked by major browsers and root programs. eMudhra has communicated the revocation to downstream trust stores. Clients and organizations should ensure their software and trust stores are updated to remove trust in the affected intermediate certificates. Mozilla has published a tool to check if clients still trust the compromised certificates. No further action is required if trust stores are updated, as the issue is effectively mitigated by revocation and blocking.