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.

The remote Ubuntu 20.04 LTS / 24.04 LTS / 26.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-8429-1 advisory.

    It was discovered that FastNetMon incorrectly validated prefix lengths when decoding BGP NLRI data. A     remote attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This     issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-48686)

    It was discovered that FastNetMon incorrectly sanitized input in the Juniper router integration plugin. An     attacker could possibly use this issue to execute arbitrary commands. (CVE-2026-48687)

    It was discovered that FastNetMon incorrectly handled buffer bounds checks when processing network     traffic. A remote attacker could possibly use this issue to cause a denial of service or execute arbitrary     code. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-48689)

    It was discovered that FastNetMon incorrectly handled encoding the BGP AS_PATH attribute. A remote     attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This issue     only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-48691)

    It was discovered that FastNetMon incorrectly validated IP address input in the Juniper router integration     plugin. An attacker could possibly use this issue to inject arbitrary router configuration commands.
    (CVE-2026-48694)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-48691)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
321184	Ubuntu 20.04 LTS / 24.04 LTS / 26.04 LTS : FastNetMon vulnerabilities (USN-8429-1)	Nessus	Ubuntu Local Security Checks	critical
317199	Linux Distros Unpatched Vulnerability : CVE-2026-48691	Nessus	Misc.	critical

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CVE-2026-48691

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