CVE-2026-48691
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 · uneditedFastNetMon Community Edition through 1.2.9 contains an integer overflow in the BGP AS_PATH attribute encoder. In src/bgp_protocol.hpp, the IPv4UnicastAnnounce::get_attributes() function computes attribute_length as 'sizeof(bgp_as_path_segment_element_t) + this->as_path_asns.size() * sizeof(uint32_t)' and stores it in a uint8_t field (line 600-605). Since uint8_t can only hold values 0-255, an AS_PATH containing more than 63 ASNs (2 + 64*4 = 258 > 255) causes silent truncation. The truncated length is used for buffer sizing, while the actual data written is the full untruncated amount, resulting in a heap buffer overflow. Similarly, the path_segment_length field at line 621 is also uint8_t, truncating with more than 255 ASNs.
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 confidenceFastNetMon Community Edition through 1.2.9 has a heap buffer overflow in the BGP AS_PATH attribute encoder. The code computes attribute_length as sizeof(bgp_as_path_segment_element_t) + as_path_asns.size() * sizeof(uint32_t) but stores it in a uint8_t field which can only hold 0-255. When AS_PATH contains more than 63 ASNs (causing computed length >255), silent truncation occurs; the truncated value is used for buffer sizing while full data is written, causing heap overflow. The path_segment_length field at line 621 has the same issue for >255 ASNs.
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<= 1.2.9CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Verify FastNetMon installation and versionRun 'fastnetmon --version' or check package manager for installed version (dpkg -l | grep fastnetmon or rpm -qi fastnetmon)Affected if Version is 1.2.9 or lower
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Confirm BGP feature is enabledCheck configuration file (typically /etc/fastnetmon.conf) for 'enable_bgp' or 'bgp_enabled' setting set to 'true' or 'yes'Affected if BGP processing is enabled in FastNetMon configuration
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Verify BGP peer/adjacency is configuredLook for 'bgp_peer' or 'bgp_neighbors' entries in fastnetmon.conf or check if BGP listening port (typically 179) is in use with 'netstat -tulpn | grep 179'
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Inspect AS_PATH attribute handling in logsReview FastNetMon logs for any warnings or errors related to BGP AS_PATH processing or attribute encoding
FastNetMon version 1.2.9 or earlier with BGP enabled and configured to process BGP AS_PATH attributes containing more than 63 ASNs is vulnerable to heap buffer overflow via integer truncation.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor dataUpgrade to a version after 1.2.9 if available, or implement input validation to reject AS_PATH attributes exceeding 63 ASNs at the parsing stage as a compensating control until the code fix is applied.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-48691 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-48691 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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