The Apache Qpid Proton-J transport includes an optional wrapper layer to perform TLS, enabled by use of the 'transport.ssl(...)' methods. Unless a verification mode was explicitly configured, client and server modes previously defaulted as documented to not verifying a peer certificate, with options to configure this explicitly or select a certificate verification mode with or without hostname verification being performed. The latter hostname verifying mode was not implemented in Apache Qpid Proton-J versions 0.3 to 0.29.0, with attempts to use it resulting in an exception. This left only the option to verify the certificate is trusted, leaving such a client vulnerable to Man In The Middle (MITM) attack. Uses of the Proton-J protocol engine which do not utilise the optional transport TLS wrapper are not impacted, e.g. usage within Qpid JMS. Uses of Proton-J utilising the optional transport TLS wrapper layer that wish to enable hostname verification must be upgraded to version 0.30.0 o…

The C client and C-based client bindings in the Apache Qpid Proton library before 0.13.1 on Windows do not properly verify that the server hostname matches a domain name in the subject's Common Name (CN) or subjectAltName field of the X.509 certificate when using the SChannel-based security layer, which allows man-in-the-middle attackers to spoof servers via an arbitrary valid certificate.

The (1) proton.reactor.Connector, (2) proton.reactor.Container, and (3) proton.utils.BlockingConnection classes in Apache Qpid Proton before 0.12.1 improperly use an unencrypted connection for an amqps URI scheme when SSL support is unavailable, which might allow man-in-the-middle attackers to obtain sensitive information or modify data via unspecified vectors.