Problem website: https://www.cacert.org
Browser: Firefox 49.0.2
Plugin ver: 2.2.0.2.1
Settings:  Without resolver, enable TLSA validation, use browser certificate 
chain

Hi,

When trying to access the CACert website the plugin shows a validation failure.

The website's certificate is issued by a sub-ca, which is itself issued by "CA 
Cert Signing Authority" (attached); the browser trusts both Root and 
subordinate CA.
The TLSA record (type 2) includes this certificate however the plugin claims 
that TLSA validation has failed and that the certificate does not correspond to 
the TLSA record.

I've extracted the Root certificate from my browser and confirmed that it 
creates an matching TLSA record by using the TLSA generator here: 
https://www.huque.com/bin/gen_tlsa

When the root/subordinate certificates are removed from Firefox it uncovers the 
error "SEC_ERROR_CERT_SIGNATURE_ALGORITHM_DISABLED", the RootCA signature uses 
md5RSA - normally roots don't need signature verification as they're 
self-signed & trusted manually, does DANE change this model; could that impact 
TLSA validation? (If so propagating the underlying error information into the 
"more info" bubble could be useful)

The issue seems somehow related to the Firefox' trust settings on the 
certificate chain, If you trust both the Class 1 Root CA, and the Class 3  
http://www.cacert.org/index.php?id=3 the error occurs, however if you only 
trust the Class 1 Root, and install Class3 without selecting any of the trust 
options the error does not occur.

Hope this gives you enough info to reproduce the problem, and identify if it's 
a bug in the validator plugin or Firefox ( or something specific to the CACert 
PKI chain )

Thanks
Chris

Attachment: CACertSigningAuthority.crt
Description: CACertSigningAuthority.crt

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