CVE-2026-48690 affects FastNetMon Community Edition through version 1.2.9 due to an integer overflow in the allocate_buffer() function within src/packet_storage.hpp. The function calculates the memory size for packet capture buffers using 32-bit unsigned arithmetic: memory_size_in_bytes = buffer_size_in_packets * (max_captured_packet_size + sizeof(fastnetmon_pcap_pkthdr_t)) + sizeof(fastnetmon_pcap_file_header_t). Given max_captured_packet_size=1500 and fastnetmon_pcap_pkthdr_t size of 16 bytes, each packet requires about 1516 bytes. If buffer_size_in_packets exceeds roughly 2,832,542, the multiplication overflows, resulting in a smaller buffer allocation than intended. Subsequent write_packet() operations then write beyond the allocated buffer, causing heap corruption. The buffer_size_in_packets is derived from the ban_details_records_count configuration parameter, which is parsed using atoi() without overflow checks, allowing an attacker to trigger this condition. The vulnerability is classified under CWE-190 (Integer Overflow) and CWE-122 (Heap-based Buffer Overflow).

Successful exploitation can lead to heap corruption, which may allow an attacker with local privileges to compromise confidentiality and integrity of the system. The CVSS vector indicates low attack complexity and privileges required, no user interaction, and impacts on confidentiality and integrity but not availability. There are no known exploits in the wild at this time.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should avoid setting the ban_details_records_count configuration parameter to values that could cause the integer overflow (i.e., values exceeding approximately 2,832,542). Monitoring configuration inputs for unusually large values may help mitigate risk. No official patch or workaround has been documented as of now.