# CVE-2026-100664: Netty 4.2.2 through 4.2.17 HTTP/1 Host Header Authority Confusion

> Netty HTTP/3 codec mishandles Host headers, allowing authority confusion in proxies that bypass routing or authorization checks.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/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-gjrj-m8xc-f2cm, GHSA-hfr2-x62w-v49h, UBUNTU-CVE-2026-100664

## What is CVE-2026-100664?

CVE-2026-100664 is a high-severity 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) versions 4.2.2.Final through 4.2.17.Final builds the HTTP/3 :authority pseudo-header from the HTTP/1 Host header before considering the authority of an absolute-form HTTP/1 request-target. In HttpConversionUtil.toHttp3Headers(HttpMessage, boolean) — reached via Http3FrameToHttpObjectCodec(false) — a non-empty Host header takes precedence over the request-target authority, contrary to the HTTP/1.1 rule that a server receiving an absolute-form request-target must ignore the Host header. In a Netty-based HTTP/1-to-HTTP/3 gateway, proxy, or protocol bridge, a remote client can send a request such as "GET https://trusted.example/admin HTTP/1.1" with "Host: attacker.example", causing components that validate, authorize, or route on the RFC-defined request-target authority to reach a different decision than the upstream HTTP/3 peer, which receives :authority derived from the conflicting Host header. This authority confusion can affect virtual-host routing, allow-list checks, backend selection, cache keys, and URL generation. The advisory reports integrity impact only (no code execution, memory corruption, or availability impact). Fixed in 4.2.18.Final.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-100664?


## How do I fix CVE-2026-100664?

No fix has been published for CVE-2026-100664 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100664 being exploited?

There is no known exploitation of CVE-2026-100664 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100664 and fix it if it is affected.

What it is: CVE-2026-100664 is a high-severity 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: There is no known exploitation of CVE-2026-100664 in the wild and no public exploit code.

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-2026-100664/ (Markdown: https://insights.sbomify.com/CVE-2026-100664/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100664
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100664
- OSV: https://osv.dev/vulnerability/CVE-2026-100664

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100664/
Summaries are generated and may contain mistakes; the official description above is the record.