CriticalFix available

fastnetmon — security advisory

Type: advisorySources: OSVAdvisory ID: UBUNTU-CVE-2026-48686

FastNetMon Community Edition through 1.2.9 contains a stack-based buffer overflow in the BGP NLRI (Network Layer Reachability Information) decoder. The function decode_bgp_subnet_encoding_ipv4_raw() in src/bgp_protocol.cpp reads prefix_bit_length directly from the BGP packet (line 99) without validating it is <= 32 for IPv4 prefixes. This value is passed to how_much_bytes_we_need_for_storing_certain_subnet_mask() which computes ceil(prefix_bit_length / 8), returning up to 32 bytes for a prefix_bit_length of 255. The result is used as the length argument to memcpy() (line 106), which copies into a 4-byte uint32_t stack variable (prefix_ipv4). This causes a stack buffer overflow of up to 28 bytes, which can be exploited for arbitrary code execution. Additionally, the unvalidated prefix_bit_length is passed to convert_cidr_to_binary_netmask_local_function_copy() (line 111), where a shift of (32 - cidr) with cidr > 32 causes undefined behavior.

Products: fastnetmon
Affected versions: 1.2.5-1, 1.2.6-1, 1.2.6-1build1, 1.2.6-1build2, 1.2.6-1build3, 1.2.6-1build4, 1.2.8+git20250911-1, 1.2.8+git20250911-1build1, 1.2.8+git20250911-1build2, 1.2.8+git20250911-2, 1.2.8-1build1, 1.2.8-1build2, 1.2.9-1, 1.2.9-1build1, 1.2.9-1build2
Fixed versions: 1.2.6-1ubuntu0.1~esm1, 1.2.8+git20250911-2ubuntu0.1~esm1
CVEs: CVE-2026-48686
Confirmed fixed CVEs: Not specified
Updated in this feed: 31 Oct 2026, 02:21 UTC · Revision 1

Source evidence

UBUNTU-CVE-2026-48686

core-osv · Original source

Published 26 May 2026, 16:16 UTC

osv:UBUNTU-CVE-2026-48686

fastnetmon

Fixed versions: 1.2.6-1ubuntu0.1~esm1

fastnetmon

Fixed versions: Not specified

fastnetmon

Fixed versions: Not specified

fastnetmon

Fixed versions: 1.2.8+git20250911-2ubuntu0.1~esm1

Complete source record

{
  "id": "9bc9ce9566468648ccf5e632f0d5f344faea3b876b1c65b5a60fa07f685c0ea7",
  "url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-48686",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "UBUNTU-CVE-2026-48686",
    "summary": "FastNetMon Community Edition through 1.2.9 contains a stack-based buffer overflow in the BGP NLRI (Network Layer Reachability Information) decoder. The function decode_bgp_subnet_encoding_ipv4_raw() in src/bgp_protocol.cpp reads prefix_bit_length directly from the BGP packet (line 99) without validating it is <= 32 for IPv4 prefixes. This value is passed to how_much_bytes_we_need_for_storing_certain_subnet_mask() which computes ceil(prefix_bit_length / 8), returning up to 32 bytes for a prefix_bit_length of 255. The result is used as the length argument to memcpy() (line 106), which copies into a 4-byte uint32_t stack variable (prefix_ipv4). This causes a stack buffer overflow of up to 28 bytes, which can be exploited for arbitrary code execution. Additionally, the unvalidated prefix_bit_length is passed to convert_cidr_to_binary_netmask_local_function_copy() (line 111), where a shift of (32 - cidr) with cidr > 32 causes undefined behavior.",
    "evidence": "osv:UBUNTU-CVE-2026-48686",
    "products": [
      {
        "name": {
          "value": "fastnetmon",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.2.6-1ubuntu0.1~esm1",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "1.2.5-1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.2.6-1",
            "evidence": "/affected/0/versions"
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          {
            "value": "1.2.6-1build1",
            "evidence": "/affected/0/versions"
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          {
            "value": "1.2.6-1build2",
            "evidence": "/affected/0/versions"
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          {
            "value": "1.2.6-1build3",
            "evidence": "/affected/0/versions"
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          {
            "value": "1.2.6-1build4",
            "evidence": "/affected/0/versions"
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      {
        "name": {
          "value": "fastnetmon",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": [
          {
            "value": "1.2.8-1build1",
            "evidence": "/affected/1/versions"
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          {
            "value": "1.2.8-1build2",
            "evidence": "/affected/1/versions"
          },
          {
            "value": "1.2.8+git20250911-1",
            "evidence": "/affected/1/versions"
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        ]
      },
      {
        "name": {
          "value": "fastnetmon",
          "evidence": "/affected/2/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": [
          {
            "value": "1.2.8+git20250911-2",
            "evidence": "/affected/2/versions"
          },
          {
            "value": "1.2.9-1",
            "evidence": "/affected/2/versions"
          },
          {
            "value": "1.2.9-1build1",
            "evidence": "/affected/2/versions"
          },
          {
            "value": "1.2.9-1build2",
            "evidence": "/affected/2/versions"
          }
        ]
      },
      {
        "name": {
          "value": "fastnetmon",
          "evidence": "/affected/3/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.2.8+git20250911-2ubuntu0.1~esm1",
            "evidence": "/affected/3/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "1.2.8+git20250911-1",
            "evidence": "/affected/3/versions"
          },
          {
            "value": "1.2.8+git20250911-1build1",
            "evidence": "/affected/3/versions"
          },
          {
            "value": "1.2.8+git20250911-1build2",
            "evidence": "/affected/3/versions"
          },
          {
            "value": "1.2.8+git20250911-2",
            "evidence": "/affected/3/versions"
          }
        ]
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "UBUNTU-CVE-2026-48686",
      "aliases": [
        "UBUNTU-CVE-2026-48686"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
        },
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
        },
        {
          "type": "Ubuntu",
          "score": "medium"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.2.6-1ubuntu0.1~esm1"
                }
              ]
            }
          ],
          "package": {
            "name": "fastnetmon",
            "purl": "pkg:deb/ubuntu/fastnetmon?arch=source&distro=esm-apps%2Fnoble",
            "ecosystem": "Ubuntu:Pro:24.04:LTS"
          },
          "versions": [
            "1.2.5-1",
            "1.2.6-1",
            "1.2.6-1build1",
            "1.2.6-1build2",
            "1.2.6-1build3",
            "1.2.6-1build4"
          ],
          "database_specific": {
            "source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-48686.json"
          },
          "ecosystem_specific": {
            "binaries": [
              {
                "binary_name": "fastnetmon",
                "binary_version": "1.2.6-1ubuntu0.1~esm1"
              }
            ],
            "availability": "Available with Ubuntu Pro: https://ubuntu.com/pro"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                }
              ]
            }
          ],
          "package": {
            "name": "fastnetmon",
            "purl": "pkg:deb/ubuntu/fastnetmon?arch=source&distro=questing",
            "ecosystem": "Ubuntu:25.10"
          },
          "versions": [
            "1.2.8-1build1",
            "1.2.8-1build2",
            "1.2.8+git20250911-1"
          ],
          "database_specific": {
            "source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-48686.json"
          },
          "ecosystem_specific": {
            "binaries": [
              {
                "binary_name": "fastnetmon",
                "binary_version": "1.2.8+git20250911-1"
              }
            ]
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                }
              ]
            }
          ],
          "package": {
            "name": "fastnetmon",
            "purl": "pkg:deb/ubuntu/fastnetmon?arch=source&distro=stonking",
            "ecosystem": "Ubuntu:26.10"
          },
          "versions": [
            "1.2.8+git20250911-2",
            "1.2.9-1",
            "1.2.9-1build1",
            "1.2.9-1build2"
          ],
          "database_specific": {
            "source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-48686.json"
          },
          "ecosystem_specific": {
            "binaries": [
              {
                "binary_name": "fastnetmon",
                "binary_version": "1.2.9-1build2"
              }
            ]
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.2.8+git20250911-2ubuntu0.1~esm1"
                }
              ]
            }
          ],
          "package": {
            "name": "fastnetmon",
            "purl": "pkg:deb/ubuntu/fastnetmon?arch=source&distro=esm-apps%2Fresolute",
            "ecosystem": "Ubuntu:Pro:26.04:LTS"
          },
          "versions": [
            "1.2.8+git20250911-1",
            "1.2.8+git20250911-1build1",
            "1.2.8+git20250911-1build2",
            "1.2.8+git20250911-2"
          ],
          "database_specific": {
            "source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-48686.json"
          },
          "ecosystem_specific": {
            "binaries": [
              {
                "binary_name": "fastnetmon",
                "binary_version": "1.2.8+git20250911-2ubuntu0.1~esm1"
              }
            ],
            "availability": "Available with Ubuntu Pro: https://ubuntu.com/pro"
          }
        }
      ],
      "modified": "2026-10-17T12:58:30.511920739Z",
      "provider": "osv",
      "upstream": [
        "CVE-2026-48686"
      ],
      "references": [
        "https://ubuntu.com/security/CVE-2026-48686",
        "https://www.cve.org/CVERecord?id=CVE-2026-48686",
        "https://lorikeetsecurity.com/blog/fastnetmon-cve-2026-48686-bgp-nlri-stack-overflow",
        "https://github.com/pavel-odintsov/fastnetmon/pull/1053",
        "https://github.com/pavel-odintsov/fastnetmon/commit/265a767635767d7a08391dbe7f98f750d2ea04d0",
        "https://github.com/pavel-odintsov/fastnetmon",
        "https://github.com/pavel-odintsov/fastnetmon/blob/master/src/bgp_protocol.cpp",
        "https://ubuntu.com/security/notices/USN-8429-1"
      ]
    },
    "related_cves": [
      {
        "value": "CVE-2026-48686",
        "evidence": "/upstream"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 358675,
  "published_at": "2026-05-26T16:16:00+00:00"
}