An integer underflow vulnerability exists in the `nextstate()` function in `gpsd/packet.c` of...

An integer underflow vulnerability exists in the nextstate() function in gpsd/packet.c of gpsd versions prior to commit ffa1d6f40bca0b035fc7f5e563160ebb67199da7. When parsing a NAVCOM packet, the payload length is calculated using lexer->length = (size_t)c - 4 without checking if the input byte c is less than 4. This results in an unsigned integer underflow, setting lexer->length to a very large value (near SIZE_MAX). The parser then enters a loop attempting to consume this massive number of bytes, causing 100% CPU utilization and a Denial of Service (DoS) condition.