OpenSSL 1.0.1 fails to recognize cross-signed roots as trusted

[Niklas Keller]

Google has it's own certificate authority "Google Internet Authority G2", which is signed by "GeoTrust Global CA". GeoTrust's certificate is already in the trust stores, but it's cross-signed by an older root named "Equifax Secure Certificate Authority".

The Equifax uses a 1024 bit private key and has therefore been removed by Mozilla in their library (NSS), see https://bugzilla.mozilla.org/show_bug.cgi?id=1156844.

Issuance from 1024 bit roots has been stopped in 2010 or 2011 IIRC and 1024 bit keys are no longer safe enough, so the root has been excluded from their root program. However, Ubuntu 12.04 and 14.04 do still ship with that root in their trust store.

A bug in the currently default OpenSSL 1.0.1f (at least in 14.04) causes OpenSSL to error if that root is missing, even if the previous root certificate "GeoTrust Global CA" is already in the root and therefore trusted. It seems like it doesn't stop on the first trusted certificate but instead requires a complete chain, so requires the "Equifax Secure Certificate Authority" to be in the trust store. That behavior is fixed in OpenSSL 1.0.2.

All 1024 bit roots should be removed from the default trust stores as soon as possible. For this to work, the OpenSSL bug has to be backported first.

If this is not going to be fixed, at least in 2018, we'll have an issue, because that's the date where "Equifax Secure Certificate Authority" will expire. If Google and various other sites will not change their root to be non-cross-signed, many connections will break and fail.

Domains I know to use old cross-signed certificates: google.com, yahoo.com. I didn't do any scans, those were just the first two I tried.

The following will happen on Aug 22 2018 without a fix:

kelunik@example:~$ faketime '2018-08-23 00:00:00' openssl s_client -quiet -verify_return_error -connect google.com:443 -CApath /usr/lib/ssl/certs
depth=3 C = US, O = Equifax, OU = Equifax Secure Certificate Authority
verify error:num=10:certificate has expired
notAfter=Aug 22 16:41:51 2018 GMT
verify return:0

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Marc Deslauriers (mdeslaur)]

What versions of the openssl and ca-certificates packages have you tried this on? On what release of Ubuntu?

The following update removed 1024-bit certs:
http://www.ubuntu.com/usn/usn-2913-1/

The following update added alternate certificate chain support to openssl:
http://www.ubuntu.com/usn/usn-2913-3/

[Marc Deslauriers (mdeslaur)]

So it seems "Equifax Secure Certificate Authority" is still present in the latest ca-certificates package. Presumably once Mozilla removes it we will issue an updated ca-certificates package.

However, removing it still allows google to validate:

$ sudo rm /usr/lib/ssl/certs/Equifax_Secure_CA.pem

$ openssl s_client -quiet -verify_return_error -connect google.com:443 -CApath /usr/lib/ssl/certs
depth=2 C = US, O = GeoTrust Inc., CN = GeoTrust Global CA
verify return:1
depth=1 C = US, O = Google Inc, CN = Google Internet Authority G2
verify return:1
depth=0 C = US, ST = California, L = Mountain View, O = Google Inc, CN = google.com
verify return:1

[Niklas Keller (kelunik)]

We originally encountered that issue on Travis. After I couldn't reproduce it locally on my 15.10 machine, I downloaded Ubuntu Server 14.04 and could verify it in a VM. Seems like I forgot to install the latest updates, verified it's fixed in the latest version.

I'll notify the Travis team, so they can update their images.

Thanks!

[Niklas Keller (kelunik)]

Didn't you forget to rehash the certificates? But nevertheless, it's working without the root and with a fresh rehash.

Found your patch, but didn't find a bug related to the patch. Don't know whether this should be closed as invalid or duplicate.

[Marc Deslauriers (mdeslaur)]

Glad it's working. I didn't rehash, but that should just result in a dangling symlink which shouldn't be valid. Thanks for testing with a fresh rehash.

I'll mark this bug as a dupe of 1528645.

Thanks!