Certificate authority eMudhra has revoked eight more intermediate CA certificates following an investigation into its recent certificate security incident. The new revocations raise the total number of affected intermediate certificates to 16, which includes eight earlier certificates whose private keys were weak enough that anyone could recover them almost instantly.

Root cause: a faulty HSM migration script

According to eMudhra’s new incident report, both sets of certificates were affected by a custom Python script used in April 2025 to move private keys between hardware security modules (HSMs). The company wrote the script to transfer certificate authority keys between different HSM vendors at its facilities after delays in obtaining new hardware. HSMs are designed to generate and store cryptographic keys so that private material never leaves the device.

The script contained a bug that reduced eight ECDSA private keys to a single byte, making them trivial to recover. The same script also processed eight RSA private keys in a way that exposed sensitive key material in the memory of the host computer rather than keeping it protected inside the HSM. The RSA keys were not weakened, but eMudhra said it could not demonstrate that they were handled under its certificate policies.

Additional revocations

  • Eight RSA intermediate CA certificates were revoked on November 7, including certificates used to issue TLS and code-signing certificates.
  • Some affected RSA intermediates had been actively issuing certificates since May 2026, with the last certificate issued on November 3.
  • eMudhra says affected customer certificates have been replaced or migrated.

Missed warning signs

The investigation found that a problem in June 2025 could have exposed the flaw more than a year before its public discovery. At that time, eMudhra detected certificate revocation lists signed with keys that did not match the corresponding CA certificates. The company corrected the signing but did not investigate the underlying cause. The company also did not verify the strength of generated private keys or confirm that keys used for certification matched those created in the HSM.

Industry response

The incident was first disclosed on October 17, when a security researcher found that eight eMudhra intermediate CA private keys could be recovered by testing just 256 possible values. Mozilla, Google, Apple, and other vendors released protections to block the compromised certificates, and Microsoft issued out-of-band Windows updates on October 26 to remove trust in the affected certificate chains on systems that could not receive automatic trust updates.

eMudhra has said it will exit the publicly trusted TLS certificate business and plans to stop issuing certificates under its remaining G1 hierarchy by November 16. It has also commissioned an independent review by KPMG, with findings expected by December 4. The company says it has detected no evidence that the compromised keys were used maliciously.