HTTP Request Smuggling Affecting io.netty:netty-codec-http3 package, versions [4.2.0.Final,4.2.18.Final)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-IONETTY-20154842
- published27 Sept 2026
- disclosed26 Sept 2026
- creditVioleta Georgieva
Introduced: 26 Sep 2026
NewCVE-2026-100659 (opens in a new tab)How to fix?
Upgrade io.netty:netty-codec-http3 to version 4.2.18.Final or higher.
Overview
Affected versions of this package are vulnerable to HTTP Request Smuggling in its HTTP/3 request header handling, which does not enforce the RFC 9114 section 4.3.1 requirement that an :authority pseudo-header and a literal host header field carry the same value when both are present. An attacker can bypass routing and access control decisions taken on the request authority by sending a single HEADERS frame carrying both fields with conflicting values, leaving downstream components that consult different fields in disagreement. This requires the application to use the HTTP/3 codec and to base routing or access control on the authority.