CVE-2026-48686 Affecting fastnetmon package, versions <1.2.6-1ubuntu0.1~esm1


Severity

Recommended
medium

Based on Ubuntu security rating.

Threat Intelligence

EPSS
0.57% (43rd percentile)

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  • Snyk IDSNYK-UBUNTU2404-FASTNETMON-16913662
  • published12 Jun 2026
  • disclosed26 May 2026

Introduced: 26 May 2026

NewCVE-2026-48686  (opens in a new tab)

How to fix?

Upgrade Ubuntu:24.04 fastnetmon to version 1.2.6-1ubuntu0.1~esm1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream fastnetmon package and not the fastnetmon package as distributed by Ubuntu. See How to fix? for Ubuntu:24.04 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1