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FastnetmonApplication · Pavel Odintsov

CVE-2026-48689

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-26
Fix available
A fix is available. Upgrade to after 1.2.9 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
FastNetMon Community Edition through 1.2.9 contains an off-by-one heap-based buffer overflow in the dynamic_binary_buffer_t class (src/dynamic_binary_buffer.hpp). Five methods (append_dynamic_buffer, append_data_as_pointer, append_data_as_object_ptr, memcpy_from_ptr, memcpy_from_object_ptr) use an incorrect bounds check of the form 'if (offset + length > maximum_internal_storage_size + 1)' instead of the correct 'if (offset + length > maximum_internal_storage_size)'. This allows writing exactly one byte past the end of the heap-allocated buffer. The class is used pervasively in BGP message encoding/decoding, NetFlow template processing, and Flow Spec NLRI construction. An attacker who can send network traffic (NetFlow, sFlow, IPFIX, or BGP) to a FastNetMon instance can trigger this overflow, potentially achieving arbitrary code execution by corrupting heap metadata. Notably, the append_byte() method uses the correct bounds check, confirming the inconsistency.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

FastNetMon Community Edition through 1.2.9 has an off-by-one heap buffer overflow in dynamic_binary_buffer_t class. Five methods use an incorrect bounds check allowing exactly one byte past the buffer end. The class is used in BGP message encoding/decoding, NetFlow template processing, and Flow Spec NLRI construction. Attackers sending network traffic (NetFlow, sFlow, IPFIX, or BGP) can trigger this for potential arbitrary code execution via heap metadata corruption.

MitigationApply vendor patch when available; until then, restrict network access to FastNetMon to trusted sources only to reduce attack surface.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FastnetmonApplication
Affected:<= 1.2.9

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify FastNetMon version
    Run 'fastnetmon --version' or check /opt/fastnetmon/VERSION file, or look for version in the binary
    Affected if version is 1.2.9 or lower
  2. Check if NetFlow/sFlow/IPFIX collection is enabled
    Inspect FastNetMon configuration file (typically /etc/fastnetmon.conf) for netflow_listener, sflow_listener, or ipfix_listener options set to 'enabled' or 'on'
    Affected if any of these traffic collectors are enabled and receiving data from network sources
  3. Verify BGP processing is active
    Check configuration for 'bgp_enabled' or 'bgp_neighbors' settings in fastnetmon.conf
    Affected if BGP functionality is configured and operational
  4. Locate vulnerable source file
    If source is available, examine src/dynamic_binary_buffer.hpp and search for the five methods: append_dynamic_buffer, append_data_as_pointer, append_data_as_object_ptr, memcpy_from_ptr, memcpy_from_object_ptr
    Affected if source contains these methods with '+1' in bounds check calculations (incorrect off-by-one bounds)
  5. Review runtime logs for overflow indicators
    Check FastNetMon logs (typically /var/log/fastnetmon.log or journalctl) for segmentation faults, heap corruption warnings, or buffer-related errors occurring during traffic processing
    Affected if such errors appear after receiving network traffic from untrusted sources

Environment is affected if FastNetMon version is 1.2.9 or lower AND NetFlow/sFlow/IPFIX collection or BGP processing is enabled, allowing external network traffic to trigger the off-by-one heap overflow in the dynamic_binary_buffer_t class.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 1.2.9
Interim mitigation

Apply vendor patch when available; until then, restrict network access to FastNetMon to trusted sources only to reduce attack surface.

Recommended fix Moderate confidence

FastNetMon Community Edition 1.2.10 or later (verify exact fixed release on GitHub releases page)

  1. Check the current FastNetMon version using 'fastnetmon --version' or the package manager
  2. Consult the official FastNetMon GitHub repository (github.com/FastNetMon) to identify if version 1.2.10 or later contains the fix for the off-by-one bounds check vulnerability in src/dynamic_binary_buffer.hpp
  3. If a fixed version is available, upgrade using the standard installation method for your platform (e.g., apt update && apt install fastnetmon, or recompile from source)
  4. After upgrade, verify the version number matches the fixed release
  5. Test that critical functionality (BGP, NetFlow, sFlow, IPFIX processing) continues to operate normally
  6. Monitor logs for any anomalies during initial traffic processing
Caveat Review release notes for any configuration or feature changes between 1.2.9 and the fixed version

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fastnetmon Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing12.0 h
  • Review / QA4.0 h
26.0 hours of engineering $4,400
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-48689 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data