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high · CVSS 7.5

CVE-2026-93488

Io.netty/netty-codec-http: netty: denial of service via unbounded concurrent spdy streams

Published 18 Sept 2026 · Source updated 6 Nov 2026 · Retrieved 2026-11-06 16:38 UTC

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What happened?

A flaw was found in Netty. SpdySessionHandler accepts an unlimited number of concurrent remote-initiated streams because localConcurrentStreams defaults to Integer.MAX_VALUE and the handler provides no API to change it. A remote peer can open a SPDY connection and send a large number of SYN_STREAM frames with FLAG_FIN=0, causing unbounded heap and direct memory allocation that can lead to JVM OutOfMemoryError and a denial of service.

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-httpRed Hatunaffected: 4.1.138.Final-redhat-00001 to < *See vendor advisory
netty-codec-httpRed 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-httpRed HatDefault status: unaffectedSee vendor advisory
netty-codec-httpRed HatDefault status: unaffectedSee vendor advisory
netty-codec-httpRed HatDefault status: unaffectedSee vendor advisory
netty-codec-httpRed HatDefault status: unaffectedSee vendor advisory
netty-codec-httpRed HatDefault status: affectedSee vendor advisory
netty-codec-httpRed HatDefault status: affectedSee vendor advisory
netty-codec-httpRed HatDefault status: affectedSee vendor advisory
netty-codec-httpRed HatDefault status: affectedSee vendor advisory
netty-codec-httpRed HatDefault status: affectedSee vendor advisory
netty-codec-httpRed HatDefault status: affectedSee vendor advisory
netty-codec-httpRed HatDefault status: unknownSee vendor advisory
netty-codec-httpRed HatDefault status: unknownSee vendor advisory
netty-codec-httpRed 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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