CVE-2026-48685
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 has out-of-bounds memory access because it incorrectly parses BGP path attributes with the extended length flag set. In src/bgp_protocol.hpp, the parse_raw_bgp_attribute() function correctly identifies when extended_length_bit is set and sets length_of_length_field to 2, but then reads only a single byte for the attribute value length (attribute_value_length = value[2] at line 173). Per RFC 4271 Section 4.3, when the Extended Length bit is set, the Attribute Length field is two octets and the value should be read as a 16-bit big-endian integer from value[2] and value[3]. As a result, any attribute longer than 255 bytes has its length silently truncated to the low byte (e.g., 300 bytes = 0x012C is read as 0x2C = 44 bytes). The remaining 256 bytes are then misinterpreted as subsequent attributes, causing cascading parse failures and potential out-of-bounds memory access.
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 incorrectly parses BGP path attributes when the extended length flag is set. The parse_raw_bgp_attribute() function reads only a single byte for the attribute value length (value[2]) instead of reading a 16-bit big-endian integer from value[2] and value[3] as required by RFC 4271 Section 4.3. This causes attributes longer than 255 bytes to have their length silently truncated (e.g., 300 bytes becomes 44 bytes), leading to misinterpretation of subsequent data as new attributes and potential out-of-bounds memory access.
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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/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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Confirm FastNetMon installation and versionRun 'fastnetmon --version' or check package version with 'dpkg -l | grep fastnetmon' or 'rpm -qi fastnetmon'Affected if Version is 1.2.9 or lower
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Verify BGP processing is enabledCheck fastnetmon.conf for 'enable_bgp' or similar BGP-related settings, typically located in /etc/fastnetmon/fastnetmon.confAffected if BGP processing is explicitly enabled in the configuration file
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Check for active BGP peer configurationReview fastnetmon.conf for BGP neighbor/peer definitions or look in /etc/bgp-peers/ directory if usedAffected if BGP peers or neighbors are configured, which triggers the vulnerable attribute parsing code path
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Inspect the vulnerable function in source codeIf source is available, examine src/bgp_protocol.hpp for the parse_raw_bgp_attribute function: verify it reads only value[2] for attribute length when the extended_length_bit flag is set, rather than reading value[2] and value[3] as a 16-bit big-endian integerAffected if The code contains the single-byte length read instead of correctly reading two bytes for extended length attributes
System is affected if FastNetMon version is 1.2.9 or lower AND BGP processing with peer configuration is enabled, which triggers the flawed attribute parser that truncates extended-length BGP attributes.
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 patched version that correctly reads a 16-bit big-endian integer for attribute length when the extended length flag is set. Alternatively, implement input validation to reject BGP messages with extended length attributes that exceed expected sizes.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-48685 — 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-2026-48685 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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