---
id: CVE-2026-122129
title: CESNET ipfixcol2 2.7.1 before 2.9.0 Memory Exhaustion via TCP LZ4 Decoder
summary: >-
  CESNET ipfixcol2 2.7.1 before 2.9.0 contains a memory allocation vulnerability
  in Lz4Decoder::read_start_header() that allows unauthenticated attackers to
  exhaust memory by declaring unbounded ring buffer sizes. Attackers can open
  TCP co…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cvssSource: cna
cwe:
  - CWE-789
vendor: CESNET
product: ipfixcol2
affected:
  - ipfixcol2 >= 2.7.1 < 2.9.0
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-11-05T20:48:38.242757Z'
published: '2026-11-04'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T20:48:47.204Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-122129'
references:
  - url: >-
      https://github.com/CESNET/ipfixcol2/commit/1a199033eff847941353c5c039cb806a9ad8aa6f
    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#L126-L131
  - url: >-
      https://www.vulncheck.com/advisories/cesnet-ipfixcol2-2.7.1-before-2.9.0-memory-exhaustion-via-tcp-lz4-decoder
    label: >-
      VulnCheck Advisory: CESNET ipfixcol2 2.7.1 before 2.9.0 Memory Exhaustion
      via TCP LZ4 Decoder
tags:
  - cve.org
epss: 0.00401
epssPercentile: 0.34581
ingestedAt: '2026-11-05T22:38:31.885Z'
---

## Overview

CESNET ipfixcol2 2.7.1 before 2.9.0 contains a memory allocation vulnerability in Lz4Decoder::read_start_header() that allows unauthenticated attackers to exhaust memory by declaring unbounded ring buffer sizes. Attackers can open TCP connections sending LZ4 start headers with very large buffer sizes, forcing up to 4 GiB allocations per connection and denying collector service.

## Affected

- `ipfixcol2 >= 2.7.1 < 2.9.0`

## Remediation

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