High severity · published Jul 29, 2026
CVE-2026-59898
Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation
7.5
CVSS
0.4%
EPSS
No
On KEV
Description
Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, ab attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending `Sec-WebSocket-Version: 7` and omitting `Connection: Upgrade` / `Upgrade: websocket` headers, completing a protocol switch that a proxy would not recognize as an Upgrade request and enabling HTTP request smuggling / protocol-confusion attacks. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 38% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NE
netty · netty
>=4.2.0.Final, < 4.2.16.Final; < 4.1.136.Final · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59898
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59898
Release Notes
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
Release Notes
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final
Vendor Advisory
https://github.com/netty/netty/security/advisories/GHSA-4mp9-239f-g9hg
More from netty
7.5
CVE-2023-44487
HTTP/2 Rapid Reset Attack Vulnerability
10.0
CVE-2026-47691
Netty has Insufficient Bailiwick Validation for NS Records
10.0
CVE-2026-45674
Netty Vulnerable to DNS Cache Poisoning via Missing Bailiwick Checks in CNAME Records
9.8
CVE-2026-56817
Netty: XML External Entity (XXE) injection via unconfigured XML factory when DTD and entity processing are enabled
9.8
CVE-2026-42581
Netty: HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization