Integer Overflow or Wraparound Affecting fastnetmon package, versions <1.2.9-1


Severity

Recommended
low

Based on Debian security rating.

Threat Intelligence

EPSS
0.31% (24th percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-FASTNETMON-17087857
  • published29 May 2026
  • disclosed26 May 2026

Introduced: 26 May 2026

CVE-2026-48691  (opens in a new tab)
CWE-190  (opens in a new tab)

How to fix?

Upgrade Debian:unstable fastnetmon to version 1.2.9-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream fastnetmon package and not the fastnetmon package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1