When using the OpenSSL TLS implementation, both the pn_ssl_domain_set_trusted_ca_db() & pn_tls_config_set_trusted_certs() APIs added to rather than replaced the default system trust anchors. Leading to potentially trusting unexpected peer certificates. This can be worked around by setting the SSL_CERT_FILE environment variable for the application to /dev/null.
This issue does not affect the Win32 SChannel TLS implementation. This issue affects Apache Qpid Proton C: through 0.40.0. Users are recommended to upgrade to version 0.41.1, which fixes the issue.