Hi, Deep in the eMudhra discussion thread, Solar Designer pointed out that the Comodo AAA Services Root, which cross-signed the vulnerable eMudhra certs, is still part of NSS: https://www.openwall.com/lists/oss-security/2026/10/21/4 And Jakub pointed out that the web trust bit has been turned off: https://www.openwall.com/lists/oss-security/2026/10/21/31
I was unsure what exactly that means, and reached out to someone from Mozilla. Here's what I learned: It has "CKA_TRUST_EMAIL_PROTECTION" set, which means it is still trusted for S/MIME (in Thunderbird): https://searchfox.org/firefox-main/source/security/nss/lib/ckfw/builtins/certdata.txt#643 The eMudhra intermediates should not be able to sign S/MIME certificates. (They have an EKU extension for TLS server+client.) That is: if every S/MIME implementation out there properly checks that. My interest in S/MIME is limited, I'm probably not gonna investigate this much further. If anyone wants to look into this, the following questions may be a good starting point: * Are there other e-mail applications that source the NSS/Thunderbird cert store as their trust anchor for S/MIME? * Do they properly check X.509 paths and validate everything, or are there ones that would accept a web/TLS intermediate to sign an S/MIME cert? -- Hanno Böck https://hboeck.de/
