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high · CVSS 7.5

CVE-2026-93567

Io.netty/netty-codec-http2: http/1 authority-form connect is translated to malformed http/2 connect with host-controlled :authority

Published 18 Sept 2026 · Source updated 6 Nov 2026 · Retrieved 2026-11-06 10:44 UTC

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What happened?

A flaw was found in Netty's HTTP/2 codec. When converting HTTP/1 CONNECT requests to HTTP/2, the component incorrectly uses the Host header instead of the CONNECT authority-form request-target for the tunnel authority. A remote attacker can exploit this by supplying a different Host header, leading to a malformed HTTP/2 CONNECT request. This can bypass security controls such as tunnel allow-lists or egress policies, resulting in integrity loss.

Description supplied by CVE Program. Formatting is simplified; follow the original advisory for full details.

Affected software and versions

Source-provided software and version information
SoftwareVersion informationFixed version
io.netty/netty-codec-http2Red Hatunaffected: 4.1.138.Final-redhat-00001 to < *See vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
keycloak-rhel9-containerRed Hatunaffected: 26.4-29 to < *See vendor advisory
keycloak-rhel9-operator-bundle-containerRed Hatunaffected: 26.4.17-2 to < *See vendor advisory
keycloak-rhel9-operator-containerRed Hatunaffected: 26.4-30 to < *See vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: unaffectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory
netty-codec-http2Red HatDefault status: affectedSee vendor advisory

Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.

Is it being exploited?

This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.

CISA data retrieved 2026-11-06 16:38 UTC. Check CISA ↗

How to respond

  1. Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
  2. Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
  3. Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.

Sources and remediation references

This public advisory does not determine whether a particular server is affected. Records are refreshed as sources change; verify urgent decisions against the original advisory.

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