CVE-2026-48686

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.

USN-8429-1 — fastnetmon vulnerabilities

Affected: Ubuntu:Pro:20.04:LTS: fastnetmon, Ubuntu:Pro:24.04:LTS: fastnetmon, Ubuntu:Pro:26.04:LTS: fastnetmon

It was discovered that FastNetMon incorrectly validated prefix lengths when decoding BGP NLRI data. A remote attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-48686)

It was discovered that FastNetMon incorrectly sanitized input in the Juniper router integration plugin. An attacker could possibly use this issue to execute arbitrary commands. (CVE-2026-48687)

It was discovered that FastNetMon incorrectly handled buffer bounds checks when processing network traffic. A remote attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-48689)

It was discovered that FastNetMon incorrectly handled encoding the BGP AS_PATH attribute. A remote attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-48691)

It was discovered that FastNetMon incorrectly validated IP address input in the Juniper router integration plugin. An attacker could possibly use this issue to inject arbitrary router configuration commands. (CVE-2026-48694)

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CVE-2026-48686

USN-8429-1 — fastnetmon vulnerabilities