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CVE Record

CVE-2026-42584: Netty: HttpClientCodec response desynchronization

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

HighCVSS 7.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-42584 is a Netty HTTP client parsing flaw. Under specific response ordering, a client can match a response to the wrong request and read the stream incorrectly. This can affect confidentiality, integrity, and availability at a limited level. Fixed Netty releases are available.

Executive priority

Treat as a high-priority dependency update for internet-facing or third-party-integrating services using Netty HTTP clients. There is no provided evidence of active exploitation, but the flaw is remotely reachable and has a published fix, so remediation should be scheduled promptly.

Technical view

Before Netty 4.2.13.Final and 4.1.133.Final, HttpClientCodec can desynchronize request-response tracking when interim 1xx responses interact with pipelined GET and HEAD requests. The HEAD handling may skip a body that belongs to GET, leaving bytes on the stream and parsing later responses from the wrong offset.

Likely exposure

Exposure is most likely in Java applications or products using affected Netty or io.netty:netty-codec-http versions, directly or transitively, where HttpClientCodec processes HTTP responses from untrusted or semi-trusted servers. Systems using vendor-packaged Netty should check the listed Red Hat advisories for product-specific status.

Exploitation context

The CVSS vector indicates network reachability, low complexity, no privileges, and no user interaction. The source bundle does not show CISA KEV listing or cite active exploitation. The described condition is specific, but response desynchronization can create meaningful security impact in HTTP clients.

Researcher notes

This is CWE-444 response desynchronization in Netty HttpClientCodec queue pairing. Key research questions are where affected clients use pipelining, accept interim 1xx responses, and process HEAD/GET mixtures. Avoid assuming product exposure without dependency evidence or vendor confirmation.

Mitigation direction

  • Upgrade Netty to 4.2.13.Final, 4.1.133.Final, or later fixed releases.
  • Update io.netty:netty-codec-http where it is used directly or transitively.
  • Review Red Hat errata for affected vendor-packaged products and supported fixes.
  • Check vendor guidance before applying workarounds not named in the sources.

Validation and detection

  • Inventory applications for Netty and io.netty:netty-codec-http dependencies.
  • Inspect dependency lockfiles, SBOMs, and SCA results for affected version ranges.
  • Confirm deployed artifacts use fixed Netty versions, not only source manifests.
  • Review HTTP client code paths that use Netty HttpClientCodec.
  • Track Red Hat CSAF or errata status for packaged deployments.
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-444: Exact CWE lookup

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Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-42584 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
7.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

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
11Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: pocAutomatable: 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
7.3CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L3.93.4GitHub_M
7.3CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L3.93.4redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.3High
CVSS 3.1 vector shape for CVE-2026-42584Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
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: io.netty/netty-codec-http: Netty: Incorrect HTTP response parsing leads to data confusion
other:Red Hat severity ratingcvssV3_1
  • 2026-05-13T19:01:51.846Z: Reported to Red Hat.
  • 2026-05-13T18:10:48.437Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
nettynetty>= 4.2.0.Alpha1, < 4.2.13.Final, < 4.1.133.FinalListed
io.nettynetty-codec-http>= 4.2.0.Alpha1, < 4.2.13.Final, < 4.1.133.FinalListed
Weakness

CWE details

CWE-444

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

CWE-444 · source CWE mapping

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs