CVE-2026-42582Public exploitNetwork attack vector

HTTP/3 server crash via unchecked QPACK length

Published May 13, 2026 · Updated May 13, 2026

Memory exhaustion in Netty netty-codec-http3 before 4.2.13.Final allows remote attackers to crash HTTP/3 servers via crafted headers. QpackDecoder#decodeHuffmanEncodedLiteral allocates a byte array from the QPACK literal length before confirming that the compressed field contains that many bytes. An unauthenticated peer must reach a Netty HTTP/3 endpoint; repeated malicious HEADERS frames can stall or crash the server without affecting confidentiality or integrity.

CVSS severity7.5
High
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory exhaustion in Netty netty-codec-http3 before 4.2.13.Final allows remote attackers to crash HTTP/3 servers via crafted headers. QpackDecoder#decodeHuffmanEncodedLiteral allocates a byte array from the QPACK literal length before confirming that the compressed field contains that many bytes. An unauthenticated peer must reach a Netty HTTP/3 endpoint; repeated malicious HEADERS frames can stall or crash the server without affecting confidentiality or integrity.

The record

CVE
CVE-2026-42582
Published
May 13, 2026
Updated
May 13, 2026
Vendor
The Netty Project
Product
netty-codec-http3
Classifications
CWE-789, CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2026CVE publishedPublication date reported by the CVE source.
  2. May 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=>= 4.2.0.Alpha1, < 4.2.13.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · netty-codec-http3version=>= 4.2.0.Alpha1, < 4.2.13.Final
The Netty Project · Nettyversion=>= 4.2.0.Alpha1, < 4.2.13.Final

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-789Memory Allocation with Excessive Size Value
CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation

Public exploit references

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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