CVE-2026-48685
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Out-of-Bounds Memory Access in FastNetMon Community Edition

Publication date: 2026-05-26

Last updated on: 2026-05-27

Assigner: MITRE

Description
FastNetMon 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.
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Meta Information
Published
2026-05-26
Last Modified
2026-05-27
Generated
2026-06-16
AI Q&A
2026-05-26
EPSS Evaluated
2026-06-14
NVD
CVE-2026-48685
EUVD
EUVD-2026-31841
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
pavel-odintsov fastnetmon to 1.2.9 (inc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-130 The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.
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Executive Summary

CVE-2026-48685 is a vulnerability in FastNetMon Community Edition versions 1.2.9 and earlier where the BGP attribute parser incorrectly handles extended-length attributes.

The issue occurs in the parse_raw_bgp_attribute() function in src/bgp_protocol.hpp. When processing BGP attributes with the Extended Length flag set, which indicates a two-byte length field, the parser only reads one byte instead of two. This causes the parser to misinterpret attribute lengths, truncating the length to the low byte and treating the remaining bytes as part of subsequent attributes or phantom attributes.

This parsing error leads to cascading parse failures and potential out-of-bounds memory access, which can cause type confusion, length-field underflows, and incorrect routing decisions.

Impact Analysis

This vulnerability can impact you by causing the FastNetMon software to misinterpret BGP path attributes, leading to cascading parse failures and out-of-bounds memory access.

Such memory access issues can result in type confusion and length-field underflows, potentially destabilizing the application or causing incorrect routing decisions.

Because the vulnerability requires a trusted BGP peer and the presence of an external GoBGP daemon acting as a prefilter, exploitation is somewhat constrained, but still poses a medium risk (CVSS score 6.5).

Detection Guidance

This vulnerability can be detected by monitoring for parse errors related to BGP attributes with the extended length flag set. Since the parser misinterprets attribute lengths, observing unusual or cascading parse failures in BGP messages is a key indicator.

Additionally, constraining and filtering BGP peers and attributes at the external speaker can help identify suspicious or malformed BGP attributes that trigger this issue.

While no specific commands are provided in the resources, typical detection commands might include inspecting BGP logs for parse errors or using packet capture tools (e.g., tcpdump or Wireshark) to analyze BGP update messages for attributes with extended length flags and verifying their length fields.

Mitigation Strategies

Immediate mitigation steps include constraining BGP peers to trusted sources and filtering BGP attributes at the external speaker to prevent malformed or overly long attributes from reaching the vulnerable parser.

Capping attribute lengths to acceptable limits can reduce the risk of triggering the out-of-bounds memory access.

Monitoring parse errors closely can help detect exploitation attempts early.

As of the latest information, no vendor fix is available, so these network-level mitigations are critical.

Compliance Impact

The provided information does not specify any direct impact of CVE-2026-48685 on compliance with common standards and regulations such as GDPR or HIPAA.

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