CVE-2026-59901Network attack vector

Event-loop thread hang via malformed bzip2 stream

Published Jul 29, 2026 · Updated Jul 29, 2026

Denial of service in Netty before 4.1.136.Final and 4.2.0.Final through 4.2.15.Final allows remote attackers to hang an event-loop thread. Bzip2BlockDecompressor.read() leaves the run-length encoding state machine looping indefinitely when Bzip2Decoder processes a malformed bzip2 stream. The affected application must expose a pipeline using Bzip2Decoder to attacker-controlled compressed input; one malicious stream can permanently occupy its event-loop thread.

CVSS severity8.7
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Netty before 4.1.136.Final and 4.2.0.Final through 4.2.15.Final allows remote attackers to hang an event-loop thread. Bzip2BlockDecompressor.read() leaves the run-length encoding state machine looping indefinitely when Bzip2Decoder processes a malformed bzip2 stream. The affected application must expose a pipeline using Bzip2Decoder to attacker-controlled compressed input; one malicious stream can permanently occupy its event-loop thread.

The record

CVE
CVE-2026-59901
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-835, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 29, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=< 4.1.136.Final
  2. Affected versionversion=>=4.2.0.Final, < 4.2.16.Final

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Netty Project · Nettyversion=< 4.1.136.Final; version=>=4.2.0.Final, < 4.2.16.Final

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7GitHub, Inc.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

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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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