A flaw was found in OpenSSL. Affected versions of this package are vulnerable to Information Exposure through the SSL_select_next_proto function. This flaw allows an attacker to cause unexpected application behavior or a crash by exploiting the buffer overread condition when the function is called with a zero-length client list. This issue is only exploitable if the application is misconfigured to use a zero-length server list and mishandles the 'no overlap' response in ALPN or uses the output as the opportunistic protocol in NPN.