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A faulty Python script used to migrate keys between HSMs also affected RSA keys. eMudhra had already announced plans to exit the public TLS certificate business.
India-based certificate authority eMudhra has revoked eight additional intermediate certificates, bringing the total number affected by the security incident disclosed in October to 16. The incident initially revealed that the private keys of eight intermediate certificates could be calculated almost instantly. Attackers could have used them to issue valid certificates for any website. In a new incident report published on Mozilla’s Bugzilla platform, eMudhra has now detailed the root cause.
HSM Migration Introduced Security Flaw
According to eMudhra, both groups of certificates were affected by a custom Python script the company used in April 2025 to transfer private keys between hardware security modules (HSMs) from different vendors. HSMs are designed to securely generate and store cryptographic keys without allowing them to leave the hardware. eMudhra said it carried out the migration because of delays in the delivery of new hardware. A flaw in the script reduced eight ECDSA keys to a single byte. The same script also processed eight RSA keys, whose sensitive data was stored in the memory of the system running the script rather than being kept protected inside the HSM.
The RSA keys themselves were not weakened. However, eMudhra cannot demonstrate that they were handled in accordance with its security policies. “A re-import from the host process memory is not consistent with CPS §6.2.6, and the RSA objects are therefore treated as not meeting that requirement,” the incident report states. On November 7, eMudhra revoked the eight RSA intermediate certificates, including certificates used for TLS and code signing. Some of these certificates had actively issued certificates since May 2026, with the last issuance taking place on November 3. According to eMudhra, affected customer certificates have either been replaced or migrated.
Warning Sign Went Unnoticed
The report indicates that eMudhra could have identified the problem as early as June 2025. At the time, the company discovered that certificate revocation lists (CRLs) were being signed with keys that did not match the corresponding CA certificates. eMudhra corrected the signatures but did not investigate the underlying cause. The company also failed to verify the strength of the generated keys or check whether the certified keys matched those originally generated inside the HSM.
Withdrawal From the Public TLS Business
Following the incident, Mozilla, Google, Apple and Microsoft blocked the affected certificates. On October 26, Microsoft also released out-of-band Windows updates for systems that do not automatically receive certificate store updates. eMudhra has announced that it will withdraw from the publicly trusted TLS certificate business and migrate its customers to another provider. Under its remaining G1 hierarchy, the company will stop issuing certificates by November 16. An independent review by KPMG is expected to deliver its findings by December 4. According to eMudhra, it has found no evidence that the compromised keys were misused.
(Editorial Team)
