CVE-2026-33871Network attack vector

Service hang via unlimited zero-byte continuation frames

Published Mar 27, 2026 · Updated Mar 27, 2026

Denial of service in Netty before 4.1.132.Final and 4.2.0.Alpha1 through 4.2.9.Final allows remote attackers to hang HTTP/2 servers. DefaultHttp2FrameReader accepts unlimited CONTINUATION frames, while zero-byte payloads evade the header-size check and monopolize a CPU thread. The target must expose a Netty default HTTP/2 server; no authentication or user interaction is required, and legitimate requests become unresponsive.

CVSS severity8.7
High
EPSS probability1.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Netty before 4.1.132.Final and 4.2.0.Alpha1 through 4.2.9.Final allows remote attackers to hang HTTP/2 servers. DefaultHttp2FrameReader accepts unlimited CONTINUATION frames, while zero-byte payloads evade the header-size check and monopolize a CPU thread. The target must expose a Netty default HTTP/2 server; no authentication or user interaction is required, and legitimate requests become unresponsive.

The record

CVE
CVE-2026-33871
Published
Mar 27, 2026
Updated
Mar 27, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-770, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.1.132.Final
  2. Affected versionversion=>= 4.2.0.Alpha1, < 4.2.10.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.132.Final; version=>= 4.2.0.Alpha1, < 4.2.10.Final

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.002Service Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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