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Out-of-bounds ReadWeakness · CWE-125

CVE-2026-48683

MEDIUM · 6.5 CVSS v3.1 Published 2026-05-26
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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 out-of-bounds read vulnerability in the NetFlow v9 data flowset processor. In src/netflow_plugin/netflow_v9_collector.cpp, the Data template branch (lines 1695-1702) iterates over flow records without performing a per-iteration bounds check against the packet end pointer. In contrast, the Options template branch (lines 1709-1719) correctly checks 'if (pkt + offset + field_template->total_length > packet_end)' before each iteration. The Data branch omits this check entirely. Since template definitions are sent by the network peer (and are unauthenticated UDP), an attacker can craft templates that cause the parser to read arbitrary memory past the packet buffer. This can leak sensitive memory contents or cause a crash.

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 out-of-bounds read in the NetFlow v9 data flowset processor. The Data template branch in netflow_v9_collector.cpp iterates over flow records without validating buffer bounds before each iteration, unlike the Options template branch which properly checks 'pkt + offset + field_template->total_length > packet_end'. Since NetFlow uses unauthenticated UDP, attackers can send malicious template definitions to trigger reads beyond the packet buffer, leaking sensitive memory or causing crashes.

MitigationImplement per-iteration bounds checking in the Data template branch matching the pattern used in the Options template branch (pkt + offset + field_template->total_length <= packet_end). Consider adding template validation or rate limiting on UDP port 2055 to reduce attack surface.

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

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

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 installation and version
    Locate the FastNetMon binary or package and query its version (for example: fastnetmon --version, rpm -q fastnetmon, or dpkg -l | grep fastnetmon). Compare the returned version to the affected range: any version before 1.2.9 is vulnerable.
    Affected if The installed version is Community Edition and is earlier than 1.2.9.
  2. Verify NetFlow v9 processing is enabled
    Examine FastNetMon configuration files for NetFlow v9 settings (commonly in /etc/fastnetmon.conf or similar). Look for enable_netflow_v9, netflow_port, or related options that enable NetFlow version 9 processing.
    Affected if NetFlow v9 processing is explicitly enabled in the configuration.
  3. Confirm UDP listener is exposed to untrusted networks
    Check which UDP ports FastNetMon is listening on (typically 2055 for NetFlow). Determine if these ports are bound to interfaces accessible from untrusted networks rather than only localhost or trusted management subnets.
    Affected if FastNetMon UDP listeners accept traffic from untrusted or any network sources.
  4. Inspect for NetFlow-related crashes or anomalies
    Review system logs, FastNetMon logs, and core dumps for crashes, segfaults, or memory errors that occurred during NetFlow packet processing, especially around the time of high NetFlow v9 traffic.
    Affected if Crashes or memory errors are logged in relation to NetFlow v9 processing.

You are affected if FastNetMon Community Edition before 1.2.9 is installed, NetFlow v9 processing is enabled, and the UDP listener accepts traffic from untrusted sources.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Implement per-iteration bounds checking in the Data template branch matching the pattern used in the Options template branch (pkt + offset + field_template->total_length <= packet_end). Consider adding template validation or rate limiting on UDP port 2055 to reduce attack surface.

Recommended fix Moderate confidence
  1. Obtain the source file src/netflow_plugin/netflow_v9_collector.cpp
  2. Locate the Data template branch around lines 1695-1702
  3. Add a per-iteration bounds check before processing each flow record, similar to the Options template branch: 'if (pkt + offset + field_template->total_length > packet_end) { break; }'
  4. Recompile FastNetMon Community Edition with the patched code
  5. Redeploy the updated binary to production systems

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
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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-2026-48683 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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