---
id: "CVE-2026-122127"
kind: "vulnerability"
aliases: ["CVE-2026-122127"]
title: "ipfixcol2: LZ4 decoder heap overflow lets network peers crash the collector"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ipfixcol2", "netflow-collectors", "package", "self-hosted"]
not_affected_if: ["no-network-listener", "version-2.9.0-or-later"]
published_at: "2026-11-04T21:18:08+00:00"
first_seen_at: "2026-11-04T21:49:19+00:00"
updated_at: "2026-11-04T21:50:39+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-122127", "first_seen_at": "2026-11-04T21:49:19+00:00"}]
exploit_sources: []
---

# ipfixcol2: LZ4 decoder heap overflow lets network peers crash the collector

ipfixcol2 is a flow-data collector whose LZ4 decoder writes past a heap buffer when a crafted packet declares a small ring buffer size and a large decompressed size. An unauthenticated network peer can write up to 65535 controlled bytes and crash the collector.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed ipfixcol2 version with `ipfixcol2 --version` or the package manager, and see whether it is below `2.9.0`
- Confirm whether the collector accepts LZ4-compressed IPFIX input from the network

## Fix

- ipfixcol2 `2.9.0` (fixed version; sources state versions before 2.9.0 are affected)

## Timeline

- 2026-11-04T21:49:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-122127

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/cesnet-ipfixcol2-2.7.1-before-2.9.0-heap-buffer-overflow-via-tcp-lz4-decoder
- [fix] Patch: github.com https://github.com/CESNET/ipfixcol2/commit/fd5cb168efb4b864d33f655174711b2779cef502
- [fix] Release notes: github.com https://github.com/CESNET/ipfixcol2/releases/tag/v2.9.0

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_