CVE-2026-48691
Modified Modified - Updated After Analysis
Integer Overflow Leading to Heap Buffer Overflow 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 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.
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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-2026-48691
EUVD
EUVD-2026-31898
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-190 The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
CWE-122 A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
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Executive Summary

CVE-2026-48691 is a vulnerability in FastNetMon Community Edition up to version 1.2.9 involving an integer overflow in the BGP AS_PATH attribute encoder.

Specifically, the function IPv4UnicastAnnounce::get_attributes() uses a uint8_t field to store the length of the AS_PATH attribute. Since uint8_t can only hold values from 0 to 255, if the AS_PATH contains more than 63 ASNs, the length value is truncated silently.

This truncation causes the buffer size to be underestimated, while the actual data written exceeds this size, resulting in a heap buffer overflow.

The overflow can corrupt adjacent heap memory, potentially leading to arbitrary code execution.

Compliance Impact

CVE-2026-48691 is a high-severity heap buffer overflow vulnerability in FastNetMon Community Edition that can lead to arbitrary code execution. Such vulnerabilities can potentially be exploited to compromise the confidentiality, integrity, and availability of systems processing sensitive data.

While the provided information does not explicitly mention compliance with standards like GDPR or HIPAA, exploitation of this vulnerability could result in unauthorized access or manipulation of data, which may violate requirements for data protection and security under these regulations.

Organizations using affected versions of FastNetMon should consider this vulnerability a risk to their compliance posture and take appropriate mitigation steps to prevent exploitation.

Impact Analysis

This vulnerability can be exploited remotely via the gRPC API or BGP route forwarding by sending AS_PATH attributes with more than 63 ASNs.

Exploitation can lead to heap buffer overflow, causing heap metadata corruption and arbitrary write primitives.

As a result, an attacker could potentially execute arbitrary code on the affected system.

Detection Guidance

This vulnerability involves BGP AS_PATH attributes containing more than 63 ASNs, which causes an integer overflow and heap buffer overflow in FastNetMon Community Edition up to version 1.2.9.

To detect this vulnerability on your network or system, you should audit BGP peers for AS_PATH attributes that exceed 63 ASNs.

While no specific commands are provided in the resources, typical detection steps could include capturing BGP update messages and inspecting the AS_PATH attribute length.

  • Use packet capture tools like tcpdump or Wireshark to capture BGP traffic on port 179.
  • Filter BGP update messages and analyze the AS_PATH attribute length to identify paths with more than 63 ASNs.
  • Example tcpdump command: tcpdump -i <interface> port 179 -w bgp_traffic.pcap
  • Open the capture in Wireshark and inspect BGP update messages for AS_PATH attributes exceeding normal length.
Mitigation Strategies

Immediate mitigation steps for this vulnerability include limiting exposure and reducing the risk of exploitation until a vendor fix is available.

  • Bind the gRPC API to localhost to prevent remote exploitation via the API.
  • Audit BGP peers and filter or block routes with AS_PATH attributes longer than 63 ASNs.
  • Enable heap hardening features if supported by your environment to reduce the impact of heap buffer overflows.

A permanent fix involves updating the code to use a 16-bit integer for attribute lengths and implementing the Extended Length flag as per RFC 4271.

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