An issue was discovered in Ethernut Nut/OS 5.1. The code that generates Initial Sequence Numbers (ISNs) for TCP connections derives the ISN from an insufficiently random source. As a result, an attacker may be able to determine the ISN of current and future TCP connections and either hijack existing ones or spoof future ones. While the ISN generator seems to adhere to RFC 793 (where a global 32-bit counter is incremented roughly every 4 microseconds), proper ISN generation should aim to follow at least the specifications outlined in RFC 6528.

An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. The length byte of a domain name in a DNS query/response is not checked, and is used for internal memory operations. This may lead to successful Denial-of-Service, and possibly Remote Code Execution.

An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. The number of DNS queries/responses (set in a DNS header) is not checked against the data present. This may lead to successful Denial-of-Service, and possibly Remote Code Execution.

An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. The DNS response data length is not checked (it can be set to an arbitrary value from a packet). This may lead to successful Denial-of-Service, and possibly Remote Code Execution.

An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. There is no check on whether a domain name has '\0' termination. This may lead to successful Denial-of-Service, and possibly Remote Code Execution.