Title: FastNetMon Community Edition, Description: FastNetMon Community Edition hasta la versión 1.2.9 contiene un desbordamiento de búfer basado en pila en el decodificador BGP NLRI (Información de Alcance de Capa de Red). La función decode_bgp_subnet_encoding_ipv4_raw() en src/bgp_protocol.cpp lee prefix_bit_length directamente del paquete BGP (línea 99) sin validar que sea <= 32 para prefijos IPv4. Este valor se pasa a how_much_bytes_we_need_for_storing_certain_subnet_mask() que calcula ceil(prefix_bit_length / 8), devolviendo hasta 32 bytes para un prefix_bit_length de 255. El resultado se utiliza como argumento de longitud para memcpy() (línea 106), que copia en una variable de pila uint32_t de 4 bytes (prefix_ipv4). Esto causa un desbordamiento de búfer basado en pila de hasta 28 bytes, que puede ser explotado para ejecución de código arbitrario. Además, el prefix_bit_length no validado se pasa a convert_cidr_to_binary_netmask_local_function_copy() (línea 111), donde un desplazamiento de (32 - cidr) con cidr > 32 causa un comportamiento indefinido.

{"timestamp":"2026-05-26T20:58:47.062692Z","id":"CVE-2026-48686","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}

[{"vendor":"n/a","product":"n/a","versions":[{"version":"n/a","status":"affected"}]}]

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

OR
          *cpe:2.3:a:pavel-odintsov:fastnetmon:*:*:*:*:community:*:*:* versions up to (including) 1.2.9

MITRE: https://github.com/pavel-odintsov/fastnetmon Types: Product

MITRE: https://github.com/pavel-odintsov/fastnetmon/blob/master/src/bgp_protocol.cpp Types: Product

MITRE: https://lorikeetsecurity.com/blog/fastnetmon-cve-2026-48686-bgp-nlri-stack-overflow Types: Third Party Advisory

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE-120

CWE-787

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.

https://github.com/pavel-odintsov/fastnetmon

https://github.com/pavel-odintsov/fastnetmon/blob/master/src/bgp_protocol.cpp

https://lorikeetsecurity.com/blog/fastnetmon-cve-2026-48686-bgp-nlri-stack-overflow