Eight Intermediate CA Keys Recovered Almost Instantly
Indian certificate authority eMudhra revoked eight intermediate certificates after a researcher showed that their private keys were so weak that anyone could recover them and forge trusted certificates. Mozilla, Google, Apple, and Microsoft have all moved to block the affected certificates.
Timeline and Details
| Date (2026) | Event |
|---|---|
| Oct 17 | Researcher report reaches Mozilla; Chrome blocks the certificates |
| Oct 18 | eMudhra revokes all eight with reason caCompromise |
| Oct 19 | Apple blocks the certificates |
| Oct 20 | Microsoft blocks the certificates |
- All eight certificates use P-384 keys generated in April 2025.
- The private key values were smaller than 256, so a key could be recovered by testing only 256 candidates. One published key had a value of just 4.
- Mozilla independently recovered the keys, confirming the flaw.
- Six certificates are TLS intermediates trusted by major browser root programs; two are code-signing intermediates trusted by Microsoft.
eMudhra attributed the problem to a script error during certificate generation, which produced a second, weaker set of keys that were mistakenly selected for signing because their labels resembled the correct keys. Some certificates were also submitted to Sectigo for cross-signing.
Impact
According to reporting, no TLS certificate chaining to the six website intermediates had been logged to Certificate Transparency before Chrome's block, so none could have been trusted by default in browsers that require CT logging. The practical browser risk appears limited.
The remaining exposure is outside browsers. Clients that do not receive browser blocklists or check revocation, such as embedded devices, custom applications, and some code-signing verifiers, may still trust the affected chains until they are updated.
Recommended Actions
- Update operating systems and browsers so vendor distrust lists are applied.
- Audit trust stores in applications, appliances, and containers for eMudhra intermediates and remove them where not required.
- Review code-signing validation for artifacts chaining to the two affected code-signing intermediates.
- Check CT logs for unexpected certificates issued for your domains.
- Revisit key-generation controls if you operate a private CA: validate key entropy and range before use.