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Mozilla, Google, and Apple Block Weak eMudhra Certificates

Major browser and operating system vendors have moved quickly to block eight compromised intermediate certificates issued by certificate authority eMudhra after researchers discovered dangerously weak private keys.

Radwan AbdulhadiEditor and technology writer

Published: October 21, 2026 · Updated: October 21, 2026 · 4 min read

Mozilla, Google, and Apple Block Weak eMudhra Certificates — Image: BleepingComputer

Compromised Certificates and Weak Keys

Certificate authority eMudhra recently revoked eight compromised intermediate certificates after researchers found their private keys were remarkably weak, enabling anyone to recover them almost instantly and potentially forge trusted certificates for legitimate websites. According to a detailed account found in Mozilla's incident report, all eight affected certificates used P-384 private keys generated back in April 2025. These keys had values smaller than 256, meaning an attacker could easily recover them by testing just 256 possible numbers.

To demonstrate the severity of the flaw, security researcher Flüpke published one of the compromised private keys on GitHub, confirming that the private key for eMudhra's "EM OV TLS CA - G3C" certificate possessed a value of only 4. BleepingComputer independently verified that this published key directly matched one of the revoked certificates.

Root Cause and eMudhra's Response

When addressing the incident in a formal response to Mozilla, eMudhra attributed the vulnerability to an unexpected error in a script used during the certificate generation process in April 2025. The company explained that the script mistakenly generated a second set of weaker keys which were then accidentally selected for certificate signing because they shared labels similar to the properly generated keys. Additionally, some of the resulting certificates were submitted to Sectigo for cross-signing.

eMudhra stated that most of the impacted intermediate certificates were never actively utilized in production environments and that the company had uncovered no evidence indicating they were ever used to issue certificates to end users. Nevertheless, because these weak keys existed since their creation in April 2025, attackers theoretically could have recovered and abused them, though there remains no evidence that such exploitation occurred in the wild. Following the discovery, eMudhra promptly revoked the eight compromised certificates and halted the issuance of any new certificates under its G3 root.

Browser Vendors and Software Updates

Major software vendors reacted swiftly to mitigate the threat. Mozilla announced it successfully blocked the compromised certificates through Firefox's OneCRL system, safeguarding users immediately without requiring a manual browser update or restart. Further details regarding these protections were outlined by the organization.

Google Chrome similarly blocked the six compromised intermediates authorized to issue TLS certificates on October 17, while Apple introduced system protections shortly after on October 19. To ensure comprehensive coverage for users whose configurations might have blocked earlier revocation updates, Mozilla also released Firefox version 158.0.1 alongside corresponding updates for its ESR releases.

Other major ecosystems also took direct action. The Go development team released versions 1.27.3 and 1.26.10 specifically to address the issue, which has been officially tracked under the identifier CVE-2026-111943.

Remaining Risks and Mitigation Guidance

Despite rapid deployment of vendor patches, security experts warn that certain software utilizing custom certificate stores or lacking revocation checking capabilities may continue trusting the compromised intermediates until an update is applied. For instance, Dennis Jackson, a cryptography engineer at Mozilla, published a dedicated incident tracking website designed to list affected software along with available security updates.

Jackson specifically highlighted that macOS's built-in /usr/bin/curl utility might still trust the compromised certificates due to its default certificate bundle ignoring revocation status checks. System administrators and users are strongly advised to utilize the provided test endpoints and mitigation instructions to verify whether their systems remain vulnerable.

Installing all available software updates remains the primary recommendation for administrators and general users alike, ensuring that compromised eMudhra intermediate certificates are completely untrusted across all connected environments.