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PatchSiren cyber security CVE debrief

CVE-2026-55831 netty CVE debrief

Netty is vulnerable to a denial-of-service (DoS) attack due to improper handling of SPDY SETTINGS frames. A remote attacker can send a specially crafted SETTINGS frame to cause excessive heap growth and ordered-map insertion work, leading to a potential DoS. This issue affects Netty versions prior to 4.1.136.Final and 4.2.16.Final, and users should be aware of this vulnerability and take steps to mitigate it.

Vendor
netty
Product
Unknown
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-21
Original CVE updated
2026-07-22
Advisory published
2026-07-21
Advisory updated
2026-07-22

Who should care

Users of Netty versions prior to 4.1.136.Final and 4.2.16.Final should be aware of this vulnerability and take steps to mitigate it. This includes operators, platform administrators, vulnerability management teams, and security teams who may be impacted by the potential DoS attack.

Technical summary

The Netty SPDY SETTINGS decoder accepts a peer-declared SETTINGS entry count up to the 24-bit frame-length limit and materializes every unique setting ID in `DefaultSpdySettingsFrame`. This allows a remote SPDY/3.1 peer to send a syntactically valid roughly 2 MiB SETTINGS frame that creates 262144 map entries and amplifies network input into heap growth and ordered-map insertion work. The issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

Defensive priority

High

Recommended defensive actions

  • Update Netty to version 4.1.136.Final or 4.2.16.Final
  • Implement traffic filtering to prevent malicious SETTINGS frames
  • Monitor Netty applications for unusual traffic patterns
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-21T00:17:35.383Z and has been modified since then. The NVD entry is currently Analyzed. Evidence limits suggest that further review may be required to confirm affected scope and severity. Defenders should verify vendor guidance and assess potential impact on managed environments.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-55831 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-55831

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-55831 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-55831

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.