CVE-2026-100659 Netty 4.2.0 through 4.2.17 HTTP/3 Request Routing Bypass
Remote attackers can bypass routing and access controls in Netty HTTP/3 by sending conflicting authority headers, affecting applications using the library.
- 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-2026-100659?
CVE-2026-100659 is a medium-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) in versions 4.2.0.Final through 4.2.17.Final does not enforce the RFC 9114 requirement that the :authority pseudo-header field and a literal host header field, when both present, carry the same value. A remote unauthenticated peer can send a single HEADERS frame containing both fields with differing, attacker-controlled values; the request is accepted and delivered to the application with two conflicting authorities, allowing routing, virtual-host, and access-control decisions to be bypassed when different components in the request path consult different fields. This issue is fixed in 4.2.18.Final.
Weakness: CWE-444
Which versions are affected by CVE-2026-100659?
How do I fix CVE-2026-100659?
No fix has been published for CVE-2026-100659 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-100659 being exploited?
There is no known exploitation of CVE-2026-100659 in the wild and no public exploit code.
Sources
Also known as GHSA-7j27-hw46-m8m8, GHSA-q9pg-8h3j-8hvm, UBUNTU-CVE-2026-100659.