eMudhra, an Indian certificate authority trusted by every major web browser, has decided to stop issuing SSL/TLS certificates for websites entirely. The decision came five days after a security researcher found that eight of the company’s intermediate certificates relied on encryption keys weak enough to guess almost instantly.
Certificate authorities like eMudhra are the organizations browsers trust to vouch for a website’s identity. When a browser shows a secure connection next to a web address, it is relying on a chain of cryptographic signatures that traces back to a root certificate authority through one or more intermediate certificates. If an attacker ever obtained the private key behind one of those intermediates, they could forge a valid certificate for essentially any website and intercept supposedly secure traffic without triggering a browser warning.
That is roughly the risk researchers flagged on October 17, when they reported to Apple, Google, Microsoft, Mozilla, and eMudhra that eight of eMudhra’s intermediate certificates, six of them capable of issuing TLS certificates for websites, used private keys with numeric values below 256. A properly generated private key should be an effectively unguessable, enormous random number. A value under 256 meant a computer could find the exact key by testing, at most, 256 possibilities, which takes a fraction of a second.
Mozilla’s incident report says the flawed keys were generated in April 2025. A researcher using the handle Flüpke published one of the recovered keys publicly to demonstrate the problem, and BleepingComputer independently confirmed it matched one of the certificates eMudhra later revoked. eMudhra has said the error traces back to a script it used that April, which produced a second, weaker set of keys that were mistakenly selected for signing because their internal labels resembled the properly generated ones.
eMudhra says it has found no evidence the weak keys were ever used to issue fraudulent certificates, though it acknowledged attackers could theoretically have recovered and misused them at any point since April 2025. Google separately said no certificate from the affected intermediates appeared in the public Certificate Transparency logs before Chrome blocked them, meaning none could have been used against Chrome users specifically.
Browser makers moved quickly once the report came in. Mozilla blocked the certificates through its OneCRL revocation system on October 17, a method that takes effect without requiring users to update or restart their browser. Chrome blocked the six TLS-capable intermediates the same day. Firefox shipped point releases on October 20 for configurations that had missed the earlier block, and Apple added its own protections on October 22. Chrome has also said it will stop trusting the root certificate sitting above these intermediates, emSign ECC Root CA – G3, starting the morning of October 27.
The fallout went beyond the technical fix. On October 22, eMudhra’s board decided to exit the global SSL/TLS certificate business altogether, a market the company said accounts for only about 1 percent of its revenue. eMudhra estimated that roughly 30,000 certificates need to move to a different provider, most of them issued through the automated ACME protocol, and said it would help affected customers obtain free replacement certificates while keeping its revocation services running during the transition. Large certificate users caught up in the switch include the US higher-education certificate service InCommon, which moved onto eMudhra’s platform earlier this year. Both Cornell University and the University of Michigan have told their own certificate holders to prepare to move to alternative providers.
The incident also reopened questions about a similar problem from last year. In 2025, eMudhra had published invalid revocation lists for six of the same intermediates and said at the time that it had fixed the files by regenerating them with the correct keys. eMudhra has since told Mozilla that those 2025 files were originally signed correctly, then mistakenly re-signed using the flawed keys uncovered this month. In a public bug report, Google’s Chrome team wrote that this timeline “raises serious concerns regarding eMudhra’s transparency and incident handling.” As of Thursday afternoon UTC, eMudhra had not publicly answered a further round of questions Chrome had posted about the case.
Source: The Hacker News and BleepingComputer.
