CVE-2026-48686
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk44th percentile - higher than 44% of all known CVEs
Summary
FastNetMon Community Edition through 1.2.9 contains a stack-based buffer overflow in the BGP NLRI decoder. The function decode_bgp_subnet_encoding_ipv4_raw() in src/bgp_protocol.cpp reads prefix_bit_length directly from the BGP packet without validating it is <= 32 for IPv4 prefixes. This value is passed to how_much_bytes_we_need_for_storing_certain_subnet_mask() which computes ceil(prefix_bit_length / 8), returning up to 32 bytes for a prefix_bit_length of 255. The result is used as the length argument to memcpy() copying into a 4-byte uint32_t stack variable (prefix_ipv4), causing a stack buffer overflow of up to 28 bytes, which can be exploited for arbitrary code execution. Additionally, the unvalidated prefix_bit_length is passed to convert_cidr_to_binary_netmask_local_function_copy(), where a shift of (32 - cidr) with cidr > 32 causes undefined behavior.
Risk Assessment
A remote attacker can send a crafted BGP packet, causing a buffer overflow and potentially arbitrary code execution on the FastNetMon server, which could lead to compromise of the network monitoring system.
Recommendation
Update FastNetMon to a version above 1.2.9 that includes a fix for prefix length validation in the BGP decoder.
Original NVD description (English source)
FastNetMon Community Edition through 1.2.9 contains a stack-based buffer overflow in the BGP NLRI (Network Layer Reachability Information) decoder. The function decode_bgp_subnet_encoding_ipv4_raw() in src/bgp_protocol.cpp reads prefix_bit_length directly from the BGP packet (line 99) without validating it is <= 32 for IPv4 prefixes. This value is passed to how_much_bytes_we_need_for_storing_certain_subnet_mask() which computes ceil(prefix_bit_length / 8), returning up to 32 bytes for a prefix_bit_length of 255. The result is used as the length argument to memcpy() (line 106), which copies into a 4-byte uint32_t stack variable (prefix_ipv4). This causes a stack buffer overflow of up to 28 bytes, which can be exploited for arbitrary code execution. Additionally, the unvalidated prefix_bit_length is passed to convert_cidr_to_binary_netmask_local_function_copy() (line 111), where a shift of (32 - cidr) with cidr > 32 causes undefined behavior.