CVE-2026-59900: Netty codec-http2: Lack of Host Header Deduplication in HTTP/2→HTTP/1.x Translation Leads to Request Routing Bypass

Published Jul 22, 2026
·
Updated

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, Netty's HTTP/2-to-HTTP/1.x translation layer (Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter) fails to deduplicate or validate Host headers when an HTTP/2 client supplies both the :authority pseudo-header and a literal host header in a single HEADERS frame. The translator maps :authority to Host and separately copies the literal host header, producing an HttpRequest object containing two Host headers with attacker-controlled differing values. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

Affected Software

4 affected componentsFixes available
maven/io.netty:netty-codec-http2<4.1.136.Final
4.1.136.Final
maven/io.netty:netty-codec-http2>=4.2.0.Final<=4.2.15.Final
4.2.16.Final
Netty Netty<4.1.136
Netty Netty>=4.2.0<4.2.16

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade maven/io.netty:netty-codec-http2 to a version that resolves this vulnerability.

    Fixed in 4.1.136.Final
  2. Upgrade

    Upgrade maven/io.netty:netty-codec-http2 to a version that resolves this vulnerability.

    Fixed in 4.2.16.Final
  3. Upgrade

    Upgrade io/netty/codec-http2 to a version that resolves this vulnerability.

    Fixed in 4.1.136.Final
  4. Upgrade

    Upgrade io/netty/codec-http2 to a version that resolves this vulnerability.

    Fixed in 4.2.16.Final

Event History

Jul 22, 2026
Advisory Published
via GitHub·09:49 PM
Data Sourced
via GitHub·09:49 PM
DescriptionWeaknessAffected Software
Jul 29, 2026
CVE Published
via MITRE·05:58 PM
Data Sourced
via MITRE·05:58 PM
DescriptionWeakness
Data Sourced
via NVD·06:16 PM
DescriptionSeverityWeaknessAffected Software
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Frequently Asked Questions

1

What is the severity of CVE-2026-59900?

CVE-2026-59900 has a risk score of 43, indicating a moderate severity level.

2

How do I fix CVE-2026-59900?

To fix CVE-2026-59900, upgrade to a version of Netty that addresses this vulnerability, specifically any version post-4.1.136.Final or 4.2.16.Final.

3

What components are affected by CVE-2026-59900?

CVE-2026-59900 affects the Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter components in the Netty library.

4

What actions should be taken if CVE-2026-59900 is being exploited?

If CVE-2026-59900 is believed to be exploited, it is crucial to implement the recommended updates immediately to secure your application.

5

What types of applications are vulnerable to CVE-2026-59900?

Applications using the Netty HTTP/2 codec that inadequately handle the Host headers on incoming requests may be vulnerable to CVE-2026-59900.

Company

Resources

Contact

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