Important
Qpid Proton (C library and language bindings using it).
0.9 - 0.27.0 inclusive.
0.27.1 and later.
The TLS support in Apache Qpid Proton 0.9 - 0.27.0 can under some circumstances connect as a client to a TLS server that offers anonymous ciphers irrespective of whether the client was configured to verify the server's certificate or certificate against the hostname used to connect.
This means that an undetected man in the middle attack could be constructed if an attacker can arrange to intercept TLS traffic.
Versions 0.9 - 0.27.0 are affected when using OpenSSL prior to 1.1.0. This includes the Qpid Proton C library, and all language binding libraries using it. Installations using the native Windows Schannel TLS implementation or using OpenSSL 1.1.0 or later are not affected.
Note that this attack will not work if client certificate authentication is in use as anonymous ciphers cannot be used in this case.
Anyone using an affected version with OpenSSL prior to 1.1.0 should upgrade their installation to 0.27.1 or higher for fix to this vulnerability.
This issue was identified by the Qpid developers.
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