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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
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.
Sources
Also known as GHSA-gjrj-m8xc-f2cm, GHSA-hfr2-x62w-v49h, UBUNTU-CVE-2026-100664.