FastNetMon Community Edition versions through 1.2.9 contain a stack-based buffer overflow in the BGP NLRI decoder component. The function decode_bgp_subnet_encoding_ipv4_raw() reads the prefix_bit_length directly from the BGP packet without verifying that it is at most 32 for IPv4 prefixes. This unchecked value is used to calculate the number of bytes to copy into a fixed 4-byte stack buffer, leading to an overflow of up to 28 bytes. Additionally, the invalid prefix_bit_length is used in a bit-shift operation causing undefined behavior. The vulnerability has a CVSS 3.1 base score of 9.8, indicating critical severity with network attack vector, no privileges required, and impacts on confidentiality, integrity, and availability.

Successful exploitation of this vulnerability can result in arbitrary code execution on the affected system, compromising confidentiality, integrity, and availability. The stack buffer overflow allows an attacker to overwrite memory on the stack, potentially leading to full system compromise. The undefined behavior from invalid bit shifts may cause crashes or unpredictable behavior.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or temporary mitigation has been documented at this time. Users should monitor vendor communications for patches or updates addressing this vulnerability. Until a fix is available, consider restricting or filtering BGP traffic from untrusted sources to reduce exposure.