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Public proof of conceptFix available

CVE-2026-42587

A public proof of concept exists; no exploitation attested.

  • Published2026-05-13
  • Fixed in4.2.13 · 4.1.133
  • WeaknessCWE-400 · CWE-770

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC
  1. 2026-05-1319:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-42587?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-42587?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Netty
BranchAffectedFixed in
4.2≥ 4.2.0, < 4.2.134.2.13
4.1< 4.1.1334.1.133
netty-codec-http
BranchAffectedFixed in
4.2≥ 4.2.0.Alpha1, < 4.2.13.Final4.2.13.Final
4.1< 4.1.133.Final4.1.133.Final
netty-codec-http2
BranchAffectedFixed in
4.2≥ 4.2.0.Alpha1, < 4.2.13.Final4.2.13.Final
4.1< 4.1.133.Final4.1.133.Final

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • RHSA-2026:76128 Red Hat Product Security3 products fixed

    Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 7

  • RHSA-2026:76130 Red Hat Product Security3 products fixed

    Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 9

  • RHSA-2026:76129 Red Hat Product Security3 products fixed

    Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 8

  • RHSA-2026:76134 Red Hat Product Security3 products fixed

    Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 for OpenShift image security update

  • RHSA-2026:76132 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update

  • RHSA-2026:69459 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: AMQ Clients 2026.Q3

10 more advisories

Full record on NVD

Fix

  1. Update Netty to 4.2.13 · 4.1.133
  2. Vendor fix Red Hat Product Security RHSA-2026:76128 · 3 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
  3. Vendor fix Red Hat Product Security RHSA-2026:76134 · 3 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
  4. Vendor fix Red Hat Product Security RHSA-2026:76132 · 1 productBefore applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on. The References section of this erratum contains a download link (you must log in to download the update).
  5. Vendor fix Red Hat Product Security RHSA-2026:66545 · 1 productBefore applying the update, back up your existing installation, including all applications, configuration files, databases and database settings. The References section of this erratum contains a download link (you must log in to download the update).
  6. Vendor fix Red Hat Product Security RHSA-2026:53806 · 1 productBefore applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://acce…
  7. Vendor fix Red Hat Product Security RHSA-2026:41951 · 1 productBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionpoc2026-05-13
  • OpenCVESSVC decisionpoc—
  • CNACVSS 3.17.5read 2026-10-23
  • CNAweakness (CWE)CWE-400, CWE-770read 2026-10-23
  • FIRST EPSSEPSS score1.0 %2026-10-22
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2026-05-13
Last Modified
2026-09-18
NVD status
Modified

Frequently asked questions

What is CVE-2026-42587?

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.

Is CVE-2026-42587 actively exploited?

A proof-of-concept exploit exists for CVE-2026-42587, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-42587?

CVE-2026-42587 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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