---
id: CVE-2026-122127
title: CESNET ipfixcol2 2.7.1 before 2.9.0 Heap Buffer Overflow via TCP LZ4 Decoder
summary: >-
  CESNET ipfixcol2 2.7.1 before 2.9.0 contains a heap-based buffer overflow in
  Lz4Decoder.cpp that allows unauthenticated network peers to write past heap
  buffers. Attackers can declare a small ring buffer_size followed by a large
  decompre…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-787
vendor: CESNET
product: ipfixcol2
affected:
  - ipfixcol2 >= 2.7.1 < 2.9.0
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-11-05T19:34:44.874564Z'
published: '2026-11-04'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T19:36:14.196Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-122127'
references:
  - url: >-
      https://github.com/CESNET/ipfixcol2/commit/fd5cb168efb4b864d33f655174711b2779cef502
    label: Patch Commit
  - url: 'https://github.com/CESNET/ipfixcol2'
  - url: 'https://github.com/CESNET/ipfixcol2/releases/tag/v2.9.0'
    label: ipfixcol2 v2.9.0 Release Notes
  - url: >-
      https://github.com/CESNET/ipfixcol2/blob/v2.8.0/src/plugins/input/tcp/src/Lz4Decoder.cpp#L139-L151
  - url: >-
      https://www.vulncheck.com/advisories/cesnet-ipfixcol2-2.7.1-before-2.9.0-heap-buffer-overflow-via-tcp-lz4-decoder
    label: >-
      VulnCheck Advisory: CESNET ipfixcol2 2.7.1 before 2.9.0 Heap Buffer
      Overflow via TCP LZ4 Decoder
tags:
  - cve.org
epss: 0.00387
epssPercentile: 0.32997
ingestedAt: '2026-11-05T22:38:31.553Z'
---

## Overview

CESNET ipfixcol2 2.7.1 before 2.9.0 contains a heap-based buffer overflow in Lz4Decoder.cpp that allows unauthenticated network peers to write past heap buffers. Attackers can declare a small ring buffer_size followed by a large decompressed_size to write up to 65535 controlled bytes and crash the collector.

## Affected

- `ipfixcol2 >= 2.7.1 < 2.9.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.