---
cve: "CVE-2026-100664"
severity: "HIGH"
cvss: 8.7
epss: "0.3%"
vendor: "netty"
kev: false
exploited: false
published: "2026-09-26 14:16:49"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-29T04:47:50+02:00"
---

# CVE-2026-100664

> 8.7 HIGH · 🧪 PoC

## Beschreibung

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.

## CNA-Record (Kanon, cvelistV5)

- CNA: **VulnCheck**
- State: PUBLISHED
- Stand: 2026-09-28 16:47:05
- CNA-CVSS: **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`)

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **none**
  - Automatable: **yes**
  - Technical Impact: **partial**

## CVSS-Vektor

```
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
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Patch verfügbar (OSV)

- 2521f494432e27415a567d3a81a9eb907abf20b3 (Commit)

## BSI-Hinweise (deutsch)

- [Netty: Mehrere Schwachstellen](https://wid.cert-bund.de/portal/wid/sicherheitshinweis/WID-SEC-W-2026-3291) — _BSI-Einstufung: hoch_
  Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Netty ausnutzen, um Denial-of-Service-Zustände zu verursachen, Sicherheitsmaßnahmen zu umgehen, Request- oder Response-Smuggling durchzuführen sowie Daten offenzulegen oder zu manipulieren.

## Referenzen

- <https://github.com/netty/netty/security/advisories/GHSA-hfr2-x62w-v49h>
- <https://www.vulncheck.com/advisories/netty-4.2.2-through-4.2.15-http-1-host-header-authority-confusion>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-100664) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_