# CVE-2026-100660: Netty before 4.2.18.Final QpackEncoder Unbounded Memory Retention

> Remote attackers can cause server memory exhaustion and denial of service by exploiting unbounded QPACK encoder state retention in Netty's HTTP/3 codec.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-495p-pchh-r4mc, GHSA-8rpm-pm7h-f5fv, UBUNTU-CVE-2026-100660

## What is CVE-2026-100660?

CVE-2026-100660 is a high-severity denial of service vulnerability in netty, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.0.Final through 4.2.17.Final retains unbounded per-stream QPACK encoder state. QpackEncoder stores a queue and a dynamic-table index tracker for every encoded field section that references the QPACK dynamic table, keyed by the peer-controlled QUIC stream ID, and these entries are released only when the remote decoder sends a Section Acknowledgment or Stream Cancellation instruction — not when the HTTP/3 stream completes. There is no limit on the number of tracked streams, field sections, or retained bytes. A remote, unauthenticated HTTP/3 client can advertise a non-zero QPACK dynamic-table capacity, acknowledge the table insertion so the server reuses a dynamically indexed response header, and then omit all mandatory Section Acknowledgments while issuing sequential requests over a single QUIC connection, bypassing concurrent-stream limits and causing unbounded heap growth until the server exhausts memory (denial of service). Fixed in 4.2.18.Final.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-100660?


## How do I fix CVE-2026-100660?

No fix has been published for CVE-2026-100660 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100660 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100660 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100660 and fix it if it is affected.

What it is: CVE-2026-100660 is a high-severity denial of service vulnerability in netty, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100660 exists.

Affected product: netty. 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-2026-100660/ (Markdown: https://insights.sbomify.com/CVE-2026-100660/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100660
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100660
- OSV: https://osv.dev/vulnerability/CVE-2026-100660

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100660/
Summaries are generated and may contain mistakes; the official description above is the record.