CVE-2026-56817: Netty: XML External Entity (XXE) injection via unconfigured XML factory when DTD and entity processing are enabled

Description

Netty is a network application framework for development of protocol servers and clients. In versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, any caller that can deliver bytes to a Netty channel pipeline containing `XmlDecoder` can send XML with a `DOCTYPE` declaration to an `AsyncXMLInputFactory` instantiated with no security configuration, leaving DTD and entity handling active depending on Aalto XML async parser behavior and creating conditional XML external entity risk. This issue is 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:H/I:H/A:H

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

High

Integrity

High

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.7% · higher than 53% 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; >= 4.1.0.Final, < 4.1.136.Final · source: vendor, NVD