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CVE-2026-48685 Pavel Odintsov CVE debrief

FastNetMon Community Edition through 1.2.9 contains an out-of-bounds memory access vulnerability in its BGP path attribute parsing logic. The flaw resides in `parse_raw_bgp_attribute()` within `src/bgp_protocol.hpp`, where the function correctly identifies the extended length flag but fails to read the full 16-bit attribute length when this flag is set. Per RFC 4271 Section 4.3, extended length attributes use two octets for the length field; however, the code reads only a single byte (`value[2]`), causing values exceeding 255 bytes to be truncated to their low byte. This truncation misinterprets the remaining bytes as subsequent BGP attributes, leading to cascading parse failures and potential out-of-bounds memory access. The vulnerability is network-accessible with low attack complexity, requiring authenticated BGP session access. No known exploitation in the wild or ransomware campaign use has been reported.

Vendor
Pavel Odintsov
Product
Fastnetmon
CVSS
MEDIUM 6.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-26
Original CVE updated
2026-05-27
Advisory published
2026-05-26
Advisory updated
2026-05-27

Who should care

Network operations teams deploying FastNetMon Community Edition for DDoS detection and traffic analysis; BGP peering coordinators managing inter-domain routing infrastructure; security teams responsible for network monitoring tool hardening; and organizations relying on open-source BGP parsing implementations for production traffic analysis.

Technical summary

The vulnerability stems from incorrect implementation of RFC 4271 Section 4.3 BGP path attribute length parsing. When the Extended Length bit (bit 4 of the Attribute Flags octet) is set, the Attribute Length field expands from one octet to two octets. The affected code sets `length_of_length_field = 2` upon detecting this flag but subsequently reads `attribute_value_length = value[2]`, capturing only the high-order byte of the two-octet length. For attribute values exceeding 255 bytes (0xFF), this truncation produces incorrect length calculations—for example, a 300-byte attribute (0x012C) is interpreted as 44 bytes (0x2C). The remaining 256 bytes are then processed as additional BGP attributes, causing parser desynchronization and potential out-of-bounds memory access when subsequent length calculations reference invalid memory regions. The CVSS 3.1 score of 6.5 (Medium) reflects network accessibility and high availability impact without confidentiality or integrity compromise.

Defensive priority

medium

Recommended defensive actions

  • Upgrade FastNetMon Community Edition to a version beyond 1.2.9 when available, or apply vendor-provided patches addressing the BGP protocol parser
  • Implement BGP session authentication (MD5 or TCP-AO) to reduce unauthorized peer establishment risk
  • Monitor BGP peer sessions for anomalous attribute lengths or parsing errors that may indicate exploitation attempts
  • Restrict BGP peering to trusted, authenticated neighbors only
  • Review and validate BGP UPDATE message handling in network monitoring infrastructure for similar length-field parsing inconsistencies

Evidence notes

Vulnerability description sourced from official CVE record and NVD entry. Technical details confirmed against source references including vendor repository and security research publication. CVSS 3.1 vector AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H indicates network attack vector with low privileges required, no user interaction, and high availability impact. CWE-130 (Improper Handling of Length Parameter Inconsistency) classified as secondary weakness source.

Official resources

2026-05-26