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CVE Record

CVE-2026-42587: Netty: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpContentDecompressor accepts a maxAllocation parameter to limit decompression buffer size and prevent decompression bomb attacks. This limit is correctly enforced for gzip and deflate encodings via ZlibDecoder, but is silently ignored when the content encoding is br (Brotli), zstd, or snappy. An attacker can bypass the configured decompression limit by sending a compressed payload with Content-Encoding: br instead of Content-Encoding: gzip, causing unbounded memory allocation and out-of-memory denial of service. The same vulnerability exists in DelegatingDecompressorFrameListener for HTTP/2 connections. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This CVE can let unauthenticated internet traffic crash or exhaust memory in Netty-based services that decompress certain HTTP content encodings. The configured decompression safety limit works for gzip and deflate but is bypassed for Brotli, zstd, and snappy. The impact is availability loss, not data theft.

Executive priority

Treat as high priority for exposed services because a single unauthenticated request path may cause service outage. Patch quickly, but focus response on availability risk rather than breach containment unless other evidence emerges.

Technical view

Before Netty 4.2.13.Final and 4.1.133.Final, HttpContentDecompressor and HTTP/2 DelegatingDecompressorFrameListener ignore maxAllocation for br, zstd, and snappy. A compressed request using those encodings can trigger unbounded decompression allocation and out-of-memory denial of service. CVSS is 7.5: network, unauthenticated, low complexity, availability impact only.

Likely exposure

Exposure is most likely in Java services using Netty, netty-codec-http, or netty-codec-http2 versions below the fixed releases, especially where inbound HTTP or HTTP/2 decompression is enabled for br, zstd, or snappy.

Exploitation context

The supplied sources do not show KEV listing or active exploitation. The vulnerability is remotely reachable and unauthenticated where affected Netty decompression handlers process attacker-controlled HTTP traffic, so internet-facing services should be prioritized.

Researcher notes

The issue maps to CWE-400 and CWE-770 resource allocation controls. The affected control is maxAllocation enforcement consistency across decompression backends. Evidence provided identifies fixed Netty versions, affected modules, HTTP/1.1 and HTTP/2 paths, and Red Hat downstream tracking.

Mitigation direction

  • Upgrade Netty to 4.2.13.Final or 4.1.133.Final.
  • Update netty-codec-http and netty-codec-http2 dependencies accordingly.
  • Review Red Hat advisories for packaged product-specific fixes.
  • Check vendor guidance if upgrade timing is constrained.
  • Prioritize internet-facing HTTP and HTTP/2 services first.

Validation and detection

  • Inventory applications using Netty, netty-codec-http, or netty-codec-http2.
  • Confirm resolved dependency versions are fixed releases or later.
  • Identify services enabling inbound HTTP decompression handlers.
  • Check whether br, zstd, or snappy content encodings are accepted.
  • Verify patched builds are deployed across production instances.
Prepared
Confidence
high
Sources
6

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-400: 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.

Open ATT&CK lookup
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.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-42587 mapping review

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

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

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
14Source 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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_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 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-42587Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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: io.netty/netty-codec-http2: Netty: Denial of Service via unbounded memory allocation in HTTP content decompression
other:Red Hat severity ratingcvssV3_1
  • 2026-05-13T19:01:35.415Z: Reported to Red Hat.
  • 2026-05-13T18:22:21.699Z: 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
io.nettynetty-codec-http2>= 4.2.0.Alpha1, < 4.2.13.Final, < 4.1.133.FinalListed
Weakness

CWE details

CWE-400CWE-770

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

CWE-400 · source CWE mapping

Uncontrolled Resource Consumption

Uncontrolled Resource Consumption represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
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