An integer overflow in the FastNetMon Community Edition’s BGP AS_PATH encoder allows an attacker to craft a BGP UPDATE message with an AS_PATH containing more than 63 ASNs. The encoder treats the length of the path as a uint8_t field, truncating values above 255. The truncated length is then used to size a heap buffer, while the full untruncated attribute is copied into that buffer, causing a heap buffer overflow. The likely consequences of the buffer overflow include potential arbitrary code execution or denial of service, depending on how the overflow is exploited.

FastNetMon Community Edition software versions up to and including 1.2.9 are affected. The issue resides in src/bgp_protocol.hpp and affects the construction of IPv4UnicastAnnounce attributes during BGP message processing.

The CVSS score of 7.3 indicates high severity. The EPSS score of less than 1% suggests a low probability of exploitation, and it is not listed in the CISA KEV catalog. Nonetheless, the vulnerability remains dangerous, especially in a high‑traffic BGP environment. Based on the description, the likely attack vector is delivering a crafted BGP UPDATE packet from any reachable network to the FastNetMon instance, triggering an overflow during processing of the BGP AS_PATH attribute.