The FreeRADIUS server relies on OpenSSL to perform certificate validation,
including Certificate Revocation List (CRL) checks. The FreeRADIUS usage of
OpenSSL, in CRL application, limits the checks to leaf certificates,
therefore not detecting revocation of intermediate CA certificates.

An unexpired client certificate, issued by an intermediate CA with a revoked
certificate, is therefore accepted by FreeRADIUS.

Specifically sets the X509_V_FLAG_CRL_CHECK flag for leaf certificate CRL
checks, but does not use X509_V_FLAG_CRL_CHECK_ALL for CRL checks on the
complete trust chain.

The FreeRADIUS project advises that the recommended configuration is to use
self-signed CAs for all EAP-TLS methods.

Upstream fixes:
 - 2.x.x: https://github.com/FreeRADIUS/freeradius-server/commit/5e698b407dcac2bc45cf03484bac4398109d25c3
 - 3.0.x: https://github.com/FreeRADIUS/freeradius-server/commit/874b39451702338389260edbfc52b381b20352ec

External References:

http://freeradius.org/security.html
http://www.ocert.org/advisories/ocert-2015-008.html