eMudhra Security Flaw Exposes Trusted CA Private Keys
Indian Certificate Authority eMudhra issued eight intermediate certificates with critically weak private keys, allowing them to be recovered in seconds and potentially enabling widespread fraudulent certificate issuance.
A significant security incident has emerged involving Indian Certificate Authority (CA) eMudhra, which issued eight intermediate certificates secured with private keys so weak they could be recovered in under a second. This vulnerability, discovered by security researcher Wayne on October 17th, poses a severe risk to internet security as these compromised keys could be used to issue fraudulent HTTPS certificates for any domain.
Wayne demonstrated the flaw by signing a message with each of the compromised keys and reporting his findings to major technology companies including Apple, Google, Microsoft, and Mozilla, as well as eMudhra itself. Mozilla's Dennis Jackson publicly disclosed the incident on October 20th, highlighting that the compromised certificates chain to roots trusted by major operating systems and browsers. Cloudflare echoed these concerns, stating that the weak keys allow attackers to forge certificates and impersonate servers, thereby intercepting or modifying traffic.
The eight affected intermediate keys were part of a batch of 24 generated by eMudhra on April 30, 2025. Six of these were intended for issuing TLS certificates for websites, and two for code signing. Notably, all eight were cross-signed by certificate authority Sectigo in May 2025. The private keys, which should be extremely long random numbers, were found to be exceptionally short – some as small as the number '4', '56', or '115'. This allowed security researchers like Scott Helme to recover all of them on a standard laptop in mere seconds by testing a minimal number of values, effectively making the keys public from the moment the certificates were generated.
Major browser vendors acted swiftly to mitigate the impact. Chrome and Firefox blocked the certificates on the day of the report, followed by Apple on October 19th and Microsoft on October 20th. eMudhra itself initiated revocation of the certificates on October 18th. Despite these rapid responses, concerns remain about devices and applications that may not receive timely revocation updates, potentially leaving users vulnerable to man-in-the-middle attacks.
Mozilla took the step of removing trust in the eMudhra root certificate that signed the compromised intermediates. Google indicated it would do the same in Chrome and is conducting a thorough evaluation of eMudhra's remaining CA certificates. eMudhra has ceased issuing certificates from the affected root and estimates that approximately 30,000 customer certificates may need to be replaced. The company traced the root cause to a faulty script used during a key ceremony in April 2025, which inadvertently created a second set of weaker keys that were mistakenly used.
While eMudhra stated that only one of the compromised intermediates was put into production and none were used to issue customer certificates, the possibility that the weak keys were recovered and exploited in the 17 months between their creation and disclosure cannot be ruled out. The incident underscores the critical importance of robust key generation and management processes within Certificate Authorities.
The immediate risk to users browsing the web via major browsers has been largely contained. However, the broader implications extend to applications, servers, and devices that do not reliably update their trusted certificate lists. These systems could still implicitly trust certificates issued under the compromised keys, leaving user data exposed to interception and modification. Security experts recommend that administrators ensure their systems' certificate lists are up-to-date and that users update their browsers and operating systems to the latest versions.
This incident serves as a stark reminder of the foundational role CAs play in internet security and the cascading effects that even a single misstep in their operations can have. The ease with which these keys were recovered highlights a fundamental failure in eMudhra's security practices, necessitating a comprehensive review and overhaul of their key management and certificate issuance procedures.