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CVE Record

CVE-2026-33871: Netty HTTP/2 CONTINUATION Frame Flood DoS via Zero-Byte Frame Bypass

Netty is an asynchronous, event-driven network application framework. In versions prior to 4.1.132.Final and 4.2.10.Final, a remote user can trigger a Denial of Service (DoS) against a Netty HTTP/2 server by sending a flood of `CONTINUATION` frames. The server's lack of a limit on the number of `CONTINUATION` frames, combined with a bypass of existing size-based mitigations using zero-byte frames, allows an user to cause excessive CPU consumption with minimal bandwidth, rendering the server unresponsive. Versions 4.1.132.Final and 4.2.10.Final fix the issue.

HighCVSS 8.7Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-33871 can let an unauthenticated remote client make a Netty-based HTTP/2 server consume excessive CPU with very little traffic. The impact is service unavailability, not data theft or code execution, but exposed services could become unresponsive until fixed or protected.

Executive priority

Treat as a near-term availability risk for exposed services. Prioritize externally reachable HTTP/2 systems and business-critical Java platforms using Netty or vendor products that embed Netty.

Technical view

Affected Netty versions lack an effective limit on HTTP/2 CONTINUATION frame count. Zero-byte CONTINUATION frames can bypass size-based defenses, allowing a low-bandwidth frame flood to drive high CPU use. Fixed versions are 4.1.132.Final and 4.2.10.Final.

Likely exposure

Exposure is most likely where internet-facing or partner-facing HTTP/2 services use Netty directly or through Java frameworks, gateways, or vendor products. The bundle only identifies Netty and Red Hat downstream advisories; it does not enumerate every dependent product.

Exploitation context

The source bundle does not show CISA KEV listing or confirmed active exploitation. The attack is network-reachable, unauthenticated, low-complexity, and targets availability, so exploitation would be plausible against exposed vulnerable HTTP/2 endpoints.

Researcher notes

This is CWE-770 resource exhaustion. The key detail is count-based CONTINUATION frame handling, not header size alone. Avoid assuming all Netty users are exposed; validate HTTP/2 server usage and exact dependency versions.

Mitigation direction

  • Upgrade Netty 4.1.x to 4.1.132.Final or later.
  • Upgrade Netty 4.2.x to 4.2.10.Final or later.
  • Apply relevant Red Hat errata for Red Hat-shipped affected components.
  • Check application vendors for fixed builds when Netty is bundled transitively.
  • If upgrade is blocked, evaluate vendor-supported HTTP/2 exposure reduction.

Validation and detection

  • Inventory direct and transitive Netty dependencies across Java services.
  • Confirm deployed versions are not below 4.1.132.Final or 4.2.10.Final.
  • Identify services accepting HTTP/2 traffic at exposed edges.
  • Check Red Hat advisories for applicable product package status.
  • Review CPU saturation alerts for exposed HTTP/2 services.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-770: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-33871 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.7 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
21Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.7CVSS 4.0HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N——GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 4.0 score

8.7High
CVSS 4.0 vector shape for CVE-2026-33871Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPnetty: Netty: Denial of Service via HTTP/2 CONTINUATION frame flood
other:Red Hat severity ratingcvssV3_1
  • 2026-03-27T21:02:13.396Z: Reported to Red Hat.
  • 2026-03-27T19:55:23.135Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
nettynetty< 4.1.132.Final, >= 4.2.0.Alpha1, < 4.2.10.FinalListed
Weakness

CWE details

CWE-770

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-770 · source CWE mapping

Allocation of Resources Without Limits or Throttling

Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs