eMudhra Revokes 8 Compromised Intermediate Certificates After Private Keys Were Found to Be Guessable

Certificate authority eMudhra has revoked eight compromised intermediate certificates after researchers discovered that their private keys were so weak they could be recovered almost instantly. Attackers could have used the keys to forge trusted certificates for legitimate websites.

The affected certificates were trusted by major browsers and operating systems. If exploited, they could have allowed attackers to impersonate legitimate websites and intercept encrypted communications.

Security researcher Wayne discovered the vulnerability on October 17 while scanning publicly available certificate data.

According to Mozilla’s incident report, all eight certificates used P-384 private keys generated in April 2025 with values below 256. This meant that anyone could recover a private key by testing just 256 possible numbers.

To demonstrate the issue, security researcher Flüpke published one of the keys in a GitHub gist. The leaked key belonged to eMudhra’s “EM OV TLS CA – G3C” certificate and had a private key value of exactly 4.

BleepingComputer independently verified that the published key matches one of the revoked certificates.

In a response to Mozilla, eMudhra said the vulnerability was caused by an error in the script used to generate certificates in April 2025. According to the company, the error caused a second, weaker set of keys to be selected for certificate signing because the keys had labels similar to those of properly generated keys.

Some of the affected certificates were also submitted to Sectigo for cross-signing.

eMudhra said most of the compromised intermediate certificates were not used in production and that it found no evidence they had been used to issue certificates to end users.

However, because the certificates were created in April 2025, attackers could have recovered and exploited the weak keys before the disclosure. There is currently no evidence that this occurred.

After the issue was disclosed, eMudhra revoked all eight compromised certificates and stopped issuing new certificates from the G3 root.

Browsers and software vendors release security updates

Mozilla said that Firefox blocked the compromised certificates through its OneCRL system on October 17. This protected users without requiring browser updates or restarts.

On the same day, Google Chrome blocked six compromised intermediates that could issue TLS certificates. Apple added protections on October 19.

Mozilla also released Firefox 158.0.1 and updated ESR versions on October 20. These updates protect users whose browser settings prevent them from receiving earlier certificate-revocation updates.

Software that uses its own certificate store or does not check certificate revocation may continue to trust a compromised intermediate certificate until it receives an update.

The Go development team released Go 1.27.3 and 1.26.10 to address the issue, which is tracked as CVE-2026-111943.

Mozilla encryption engineer Dennis Jackson also said that an incident-tracking website lists affected software and available security updates.

Affected software and patched versions

Jackson warned that the /usr/bin/curl utility included with macOS may continue to trust the compromised certificates because its certificate bundles do not check revocation information.

Administrators can review the available advisories, test endpoints, and mitigation instructions to determine whether their systems remain affected.

Users and administrators should install all available software updates to ensure that the compromised certificates are no longer trusted.

The overall prevention score can hide what happens after the initial access. If an attacker uses valid credentials, your defenses drop sharply.

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