eMudhra: Eight compromised intermediate CA keys threaten TLS trust

Mozilla received a report on 17 October 2026 that private keys for eight eMudhra intermediate CA certificates had been compromised. Security researcher Scott Helme independently recovered the weak keys from the public certificates and reported that one private key was the integer 4; others included 56 and 115. This describes a very small key value, not a four-byte certificate. A holder of a compromised CA key could issue fraudulent HTTPS certificates. Intercepting a connection would also require an on-path position. The cited sources do not establish observed malicious use of these keys.

Affected intermediate CAs

Mozilla's incident record identifies six TLS issuers and two code-signing issuers. The names and CCADB identifiers are:

Use the SHA-256 certificate fingerprints in Mozilla's incident record when matching a certificate chain; a CA name alone is not a reliable cryptographic identifier.

Mozilla blocked the affected certificates through Firefox OneCRL on 17 October and released Firefox and NSS updates for clients that may not receive that block. The certifi maintainer removed the affected emSign roots from its CA bundle in version 2026.10.18.

Recommendation

• Check which browsers, libraries, containers, and custom trust stores still trust the affected certificate chain.
• Apply current browser and NSS updates; update affected certifi installations to 2026.10.18 or later and rebuild bundled images.
• Investigate any suspicious TLS certificate chains issued through the affected intermediates, while keeping observed exploitation separate from the confirmed key compromise.