Executive Summary

This vulnerability is an integer underflow in the nextstate() function of gpsd's packet.c file. When parsing a NAVCOM packet, the code calculates the payload length by subtracting 4 from an input byte value without checking if that value is less than 4. If it is, this causes an unsigned integer underflow, setting the length to a very large number. The parser then tries to process this huge length, leading to excessive CPU usage and a denial-of-service condition. [2]

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Impact Analysis

The vulnerability can cause the gpsd service to consume 100% CPU resources by entering a loop processing an extremely large payload length. This results in a denial-of-service (DoS) condition, potentially making the GPS service unavailable or unresponsive. [2]

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Detection Guidance

This vulnerability can be detected by monitoring the gpsd process for unusually high CPU utilization, as the integer underflow causes the parser to enter a loop consuming 100% CPU. You can use commands like 'top' or 'htop' on Linux to observe CPU usage of the gpsd process. Additionally, inspecting logs for malformed NAVCOM packets or unusual gpsd behavior may help. Specific commands include: 'top -p $(pidof gpsd)' or 'htop' and filtering for gpsd, and 'tcpdump' or 'wireshark' to capture and analyze NAVCOM packets for anomalies. [2, 3]

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Mitigation Strategies

The immediate mitigation step is to update gpsd to a version that includes the fix from commit ffa1d6f40bca0b035fc7f5e563160ebb67199da7, which prevents the integer underflow in the nextstate() function. Until the update can be applied, consider restricting or filtering NAVCOM packets from untrusted sources to prevent malicious packets from triggering the vulnerability. [2]

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