CVE-2026-59898Network attack vectorHinoki check available

HTTP request smuggling via lax WebSocket upgrade

Published Jul 29, 2026 · Updated Jul 29, 2026

HTTP request smuggling in Netty before 4.1.136.Final or 4.2.0.Final through 4.2.15.Final allows remote attackers to bypass proxies. The V07 and V08 handshakers accept Sec-WebSocket-Version 7 without requiring Connection: Upgrade and Upgrade: websocket, switching protocols while an intermediary still treats the exchange as HTTP. Exploitation requires an exposed WebSocket endpoint behind an intermediary that does not recognize the malformed upgrade, enabling protocol confusion and unauthorized downstream requests.

CVSS severity6.3
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

HTTP request smuggling in Netty before 4.1.136.Final or 4.2.0.Final through 4.2.15.Final allows remote attackers to bypass proxies. The V07 and V08 handshakers accept Sec-WebSocket-Version 7 without requiring Connection: Upgrade and Upgrade: websocket, switching protocols while an intermediary still treats the exchange as HTTP. Exploitation requires an exposed WebSocket endpoint behind an intermediary that does not recognize the malformed upgrade, enabling protocol confusion and unauthorized downstream requests.

The record

CVE
CVE-2026-59898
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
The Netty Project
Product
Netty
Classifications
CWE-444, T1190
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

6.3GitHub, Inc.CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A: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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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