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OSG-SEC-2026-10-23 eMudhra certificate authority key compromise

Dear OSG Security Contacts, Eight eMudhra intermediate certificate authority private keys were found to be extremely weak. The keys were created during an April 30, 2025 key generation process and were used for six TLS intermediates and two code-signing intermediates. Because the private keys could be recovered easily, someone could use them to issue fraudulent certificates. This could allow for Man-In-The-Middle (MitM) attacks on web browsers and other applications that use TLS/SSL to secure communications. [1]

WHAT ARE THE VULNERABILITIES:

What happened A flaw in a key wrapping step produced weak P-384 keys, which were then used for the eight intermediate certificates. Some private key values were only single or double-digit integers. The affected certificates were disclosed on October 17, 2026; eMudhra subsequently revoked them and stopped issuing certificates under its G3 root. The six TLS intermediates were the EV, OV, and DV variants of EM … TLS CA - G3B and - G3C. The other two were EM OV CS CA - G3B and - G3C, used for code signing. Why it matters A client that still trusts an affected TLS key could accept a fraudulent website certificate. If an attacker could intercept or redirect that client’s connection, they could impersonate the site and potentially read or alter traffic. Browser vendors blocked the affected certificates, but applications with separate or outdated trust stores may need their own updates. The two code-signing intermediates have also been blocked. Cisco Talos reported no observed malicious use as of October 21, 2026. [2]

WHAT YOU SHOULD DO (MITIGATION):

  • Update browsers, operating systems, applications, and trust stores as vendor fixes become available, especially on systems with bundled CA certificates or limited revocation checking.
  • Update affected Go applications. Go 1.26.10 and 1.27.3 add a denylist for the compromised intermediates under CVE-2026-111943.
  • Check certificates used by your services. If a certificate chains through an affected intermediate, arrange a replacement certificate and follow your CA’s guidance for deployment. A website has been set up at https://emudhra.we-have-a-problem.com/ to make it easier to detect if your own web browser or server still accepts certificates that have been issued by the compromised CAs. Refer to the section titled "Does your client still trust the compromised intermediates?" and ensure that your browser reports that it trusts 0 of the compromised certificate chains. Furthermore, running the curl commands referenced on the page from a server you want to test can verify that the certificate chains are no longer trusted by displaying an SSL connection error. [5]

REFERENCES

[1] https://www.helpnetsecurity.com/2026/10/21/emudhra-certificates-private-keys-compromised/
[2] https://blog.talosintelligence.com/compromised-intermediate-certificates/
[3] https://thehackernews.com/2026/10/eight-emudhra-ca-keys-compromised.html
[4] https://access.redhat.com/security/vulnerabilities/RHSB-2026-012
[5] https://emudhra.we-have-a-problem.com/

Please contact the OSG security team at [email protected] if you have any questions or concerns.

OSG Security Team