CVE-2023-37459: Out-of-bounds read when processing a received IPv6 packet

Contiki-NG is an operating system for internet-of-things devices. In versions 4.9 and prior, when a packet is received, the Contiki-NG network stack attempts to start the periodic TCP timer if it is a TCP packet with the SYN flag set. But the implementation does not first verify that a full TCP header has been received. Specifically, the implementation attempts to access the flags field from the TCP buffer in the following conditional expression in the checkfortcpsyn function. For this reason, an attacker can inject a truncated TCP packet, which will lead to an out-of-bound read from the packet buffer. As of time of publication, a patched version is not available. As a workaround, one can apply the changes in Contiki-NG pull request #2510 to patch the system.