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According to RFC 7685 there was at least one TLS implementation that
would hang the connection if it received a ClientHello record with a
TLSCiphertext.length between 256 and 511 bytes. During some recent testing I believe that I have come across a similar length intolerance bug. A number of servers seem to hang or close the connection if sent a ClientHello record with a TLSCiphertext.length of 266, 522, 778, ... (i.e., if TLSCiphertext.length mod 256 = 10). I have also encountered one server that will also hang the connection if sent a ClientHello record with a TLSCiphertext.length of 270, 526, 782 ... (i.e., if TLSCiphertext.length mod 256 = 14). A test for this was just added to the development branch of testssl.sh (https://github.com/drwetter/testssl.sh) -- run testssl.sh with the "--grease" option. As the server banner being returned by the servers that seem to have this problem are not all the same it is my guess that it is actually some middlebox that the is the source of the problem. Has anyone else encountered this problem? We are trying to validate that this is a real bug (https://github.com/drwetter/testssl.sh/pull/1113). Thanks, David |
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