CVE-2026-48685 Affecting fastnetmon package, versions <1.2.9-1


Severity

Recommended
low

Based on Debian security rating.

Threat Intelligence

EPSS
0.3% (22nd percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-FASTNETMON-17087856
  • published29 May 2026
  • disclosed26 May 2026

Introduced: 26 May 2026

CVE-2026-48685  (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 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.

CVSS Base Scores

version 3.1