# CVE-2026-122129: CESNET ipfixcol2 2.7.1 before 2.9.0 Memory Exhaustion via TCP LZ4 Decoder


- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 4 Nov 2026
- **Updated:** 5 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-122129, GHSA-v896-hxw5-4767, UBUNTU-CVE-2026-122129

## What is CVE-2026-122129?

CVE-2026-122129 is a medium-severity vulnerability in CESNET ipfixcol2, published on 4 Nov 2026. 

### Official description

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.

Weakness: CWE-789 (Memory Allocation with Excessive Size Value)

## Which versions are affected by CVE-2026-122129?


## How do I fix CVE-2026-122129?

Upgrade to a fixed version.

## Is CVE-2026-122129 being exploited?

There is no known exploitation of CVE-2026-122129 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-122129 and fix it if it is affected.

What it is: CVE-2026-122129 is a medium-severity vulnerability in CESNET ipfixcol2, published on 4 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-122129 in the wild and no public exploit code.

Affected product: CESNET ipfixcol2. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-122129/ (Markdown: https://insights.sbomify.com/CVE-2026-122129/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-122129
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-122129
- OSV: https://osv.dev/vulnerability/CVE-2026-122129

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-122129/
Summaries are generated and may contain mistakes; the official description above is the record.