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🛡️ CVE-2026-48686 on Ubuntu — fastnetmon

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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.

Distribution advisory

This page covers CVE-2026-48686 as tracked by Ubuntu, for the package fastnetmon. The fix is available in version 1.2.8+git20250911-2ubuntu0.1~esm1; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

UBUNTU-CVE-2026-48686 is classified as CWE-120: Classic Buffer Overflow. Input is copied into a fixed-size buffer without a length check, overwriting memory past the end of it.

Affected software

UBUNTU-CVE-2026-48686 is recorded against 1 package.

  • fastnetmon (fixed in 1.2.8+git20250911-2ubuntu0.1~esm1)

Timeline and source

Published on 26 May 2026 and last revised on 16 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

ubuntu.com (Report)
www.cve.org (Report)
lorikeetsecurity.com (Report)
github.com (Report)
github.com (Report)
github.com (Report)
github.com (Report)
ubuntu.com (Advisory)

Other advisories for this package

fastnetmon has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-120: Classic Buffer Overflow) in other software:

CVE-2026-48686 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-05-26
Updated 2026-08-20
Modified 2026-06-16
Fix URL N/A

Affected Packages

Software From version Fixed in
fastnetmon — 1.2.8+git20250911-2ubuntu0.1~esm1

Similar Threats

Exploit Protection

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UBUNTU-CVE-2026-48686 carries CVSS 9.8 Critical rating. BotEraser checks your installation against this and other known CVE records, and blocks IPs associated with exploit activity.

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