What’s Vulnerable › Vulnerabilities

CVE-2026-100659: Netty 4.2.0 through 4.2.17 HTTP/3 Request Routing Bypass

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-26 · updated 2026-09-28
• Weakness: CWE-444

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.

Affected products

• netty: from 4.2.0.Final before 4.2.18.Final — fixed in 4.2.18.Final

How to fix

Upgrade to a fixed version: netty 4.2.18.Final. Check the vendor advisory for mitigations.

References

• https://github.com/netty/netty/security/advisories/GHSA-q9pg-8h3j-8hvm
• https://www.vulncheck.com/advisories/netty-4.2.0-through-4.2.18-http-3-request-routing-bypass

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