TLS ciphersuite without mode of operation Will there be any security concern if there is no mode of operation specified in the ciphersuite name?

For instance, there is no mode of operation in TLS_ECDHE_RSA_WITH_AES_256_SHA.
It is a security issue in the sense that it likely shows that somebody doesn't know what he is doing.

TLS_ECDHE_RSA_WITH_AES_256_SHA is not an officially supported cipher suite name (internet search results too quickly degenerate for that). It probably is present in misconfigured OpenSSL servers. I presume it will default to CBC for the actual security. It is extremely unlikely to use ECB mode as that has never been a supported mode, and it would need to somehow ignore the IV if it was to be used.

Just make it the only possible cipher suite on a test server, then connect to it with a client. You'll probably find out that it is actually the CBC ciphersuite TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA with ID {0xC0, 0x14}. The ID is what is actually communicated during the handshake; the name of the ciphersuite is just what you find in the configuration parameters of the server.

It is not possible to just make up a name for a ciphersuite: it needs to resolve to an ID to be communicated within the handshake. In developers language: the ciphersuite name is an enumeration. Unfortunately OpenSSL has the nasty habit of using their own names and patterns for allowing / disallowing enumeration values.

I'd prefer a TLS 1.2 specific GCM ciphersuite and SHA-256 or SHA-512 over that particular ciphersuite.