The affected certificates were issued in April 2025, and blocked in Firefox and Chrome on October 17 by Mozilla and Google, followed by Apple on October 19 and Microsoft on October 20. Sectigo took revocation action, and Cloudflare updated its services in response.
Google stated the keys had been generated with insufficient entropy, allowing an attacker to reconstruct them and use them to create fraudulent, but otherwise valid, certificates. Although eMudhra has revoked the certificates in question and informed downstream trust stores, some systems may require software updates before ceasing to trust the compromised certificate authorities.
Mozilla’s Dennis Jackson has published a tool to help users check whether their systems trust the affected certificates, warning that “reconstructing the private keys [was] actually kind of easy” due to a severe flaw in the certificate creation process.
Jackson revealed that, aside from the final byte, all the keys were zero, and therefore could be reconstructed almost instantly using the baby-step giant-step algorithm to solve the discrete logarithm problem. He added that several people had independently managed to recover the keys.
Certificate Transparency logs have revealed no evidence of abuse of the compromised keys, but this cannot guarantee that they were not used to compromise HTTPS sites, as not all clients enforce Certificate Transparency policies. Anyone whose systems trust the compromised certificates could be at risk, as the keys could have been used to impersonate secure websites without detection.
eMudhra stated that the error was caused by a script used in the key generation ceremony which resulted in a second, weaker key pair being created. This was used to generate certificate signing requests because the labels on the keys were similar enough to mislead the process.
The company stated that the certificates in question were created for export to its data centres in the United States and Europe to satisfy data sovereignty requirements, and were not in production use, with the exception of one.
eMudhra identified human errors at several points during the process, but stated that it was investigating potential coding issues and process weaknesses, including maker-checker controls, which are meant to prevent errors by ensuring that no single individual has control over any critical process.
eMudhra has undertaken to recheck all key generation ceremonies it has performed during the coming week.
The incident demonstrates the critical importance of key generation security, internal controls and certificate revocation, and the need for organisations to update their software and trust stores following a security incident to prevent further compromises.
