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Advisory severityMedium6.5Red Hat Linux

Medium [CVE-2026-59900] Improper header neutralization in netty-codec-http2

This medium-severity Red Hat Linux advisory covers CVE-2026-59900 affecting Red Hat build of Quarkus 3.27.4.SP3, Red Hat build of Quarkus 3.33.2.SP3, Cryostat 4.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-59900 Source published Source updated

VulniPulse record published Record updated

CVE-2026-59900
Affected products & platforms
Red Hat LinuxUnclassified
Open source advisory

Summary

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. A flaw was found in Netty's netty-codec-http2 component.

The HTTP/2 encoder does not properly handle special characters in HTTP headers. This vulnerability allows a remote attacker to craft specific HTTP/2 requests, leading to HTTP response splitting and header injection attacks.

Such attacks can enable an attacker to manipulate web content or inject malicious headers. Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N).

Weakness: CWE-113.

Affected products named by the advisory: Red Hat build of Quarkus 3.27.4.SP3; Red Hat build of Quarkus 3.33.2.SP3; Cryostat 4; OpenShift Serverless; and 16 more.

Is CVE-2026-59900 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-59900 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.

How do I fix CVE-2026-59900?

Upgrade to a fixed release named by Red Hat:

  • 4.1.136
  • 4.2.16
  • io.netty/netty-codec-http2:4.1.136.Final-redhat-00001
  • RHSA-2026:47189
  • RHSA-2026:47172

Confirm against the vendor advisory before you patch.

Affected versions
  • < 4.1.136.Final
  • < 4.2.16.Final

Official advisory · high-confidence parse· fetched 3 days ago·verify at source

Fixed versions
  • 4.1.136
  • 4.2.16
  • io.netty/netty-codec-http2:4.1.136.Final-redhat-00001
  • RHSA-2026:47189
  • RHSA-2026:47172

Official advisory · high-confidence parse· fetched 3 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • - Upgrade `netty-codec-http2` to version 4.1.136.Final (4.1.x branch) or 4.2.16.Final (4.2.x branch). - If upgrading is not immediately possible, ensure that HTTP/2 traffic is routed through a reverse proxy or WAF that validates and sanitizes HTTP headers before forwarding to the Netty-based application.

Official advisory · high-confidence parse· fetched 3 days ago·verify at source

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