Summary
Certificate authority eMudhra has revoked eight additional intermediate CA certificates, bringing the total to 16, after its investigation of an earlier incident found improper private key handling during certificate generation. The new incident report was published on Bugzilla.
Root Cause
In April 2025, eMudhra used a custom Python script to move private keys between HSMs from different vendors, built after hardware delays. That script is the common factor:
- ECDSA keys: A bug reduced eight ECDSA private keys to a single byte, so anyone could recover them almost instantly. These are the eight certificates first disclosed in October.
- RSA keys: The script also handled eight RSA keys and kept their sensitive material in host process memory rather than inside the HSM. The keys were not weakened, but eMudhra could not show they met its certificate security policies, and the re-import "is not consistent with the CPS §6.2.6." They were revoked on November 7. Some of these intermediates issued TLS and code-signing certificates from May 2026, the last on November 3.
Missed Warning and Verification Gaps
In June 2025, eMudhra found CRLs signed with keys that did not match their CA certificates. It fixed the signing but did not investigate the cause. The report calls this an early warning of the faulty key-generation process. The company also did not check the strength of generated private keys or confirm that the keys used for certification matched those created in the HSM.
Discovery and Industry Response
A researcher known as "Wayne" disclosed the flaw on October 17, showing the eight intermediate private keys could be recovered by testing only 256 possible values. Mozilla, Google, Apple, and others blocked the affected certificates. Microsoft released out-of-band Windows updates on October 26 to distrust the affected chains on systems that could not receive automatic trust updates.
eMudhra's Next Steps
- Affected customer certificates have been replaced or migrated.
- eMudhra will exit the publicly trusted TLS certificate business and move remaining customers to another provider.
- It plans to stop issuing under its remaining G1 hierarchy by November 16.
- KPMG is reviewing certificate management and key-generation procedures, with findings expected by December 4.
- It says it found no evidence the compromised keys were used maliciously.
Recommended Actions
- Inventory certificates issued by eMudhra chains, including code-signing certificates, and replace any still in use.
- Keep OS and browser trust stores current so distrust updates apply.
- Plan migration for any customers still tied to eMudhra TLS issuance.
- For CA and PKI operators: never move keys through custom scripts outside the HSM boundary, and verify key strength and key-to-certificate matching after generation.