CVE-2026-56817

Analyzed Analyzed - Analysis Complete

XML External Entity Injection in Netty Framework

Publication date: 2026-07-21

Last updated on: 2026-07-30

Assigner: GitHub, Inc.

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 Scores

EPSS Scores

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Meta Information

Published

2026-07-21

Last Modified

2026-07-30

Generated

2026-08-11

AI Q&A

2026-07-22

EPSS Evaluated

2026-08-09

NVD

CVE-2026-56817

Affected Vendors & Products

Vendor	Product	Version / Range
netty	netty	From 4.1.0 (inc) to 4.1.136 (exc)
netty	netty	From 4.2.0 (inc) to 4.2.16 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-611	The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.

Attack-Flow Graph

Executive Summary

Netty versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final have a vulnerability in the XmlDecoder component. Attackers can send XML with a DOCTYPE declaration to trigger XML external entity processing if the AsyncXMLInputFactory is not configured securely. This could lead to data exposure or other attacks.

Detection Guidance

To detect this vulnerability, check if your Netty version is between 4.2.0.Final and 4.2.15.Final or 4.1.0.Final and 4.1.135.Final. Use commands like 'find / -name netty-*.jar' to locate Netty JAR files and verify their versions. If vulnerable versions are found, update to 4.1.136.Final or 4.2.16.Final or later.

Impact Analysis

If you use affected Netty versions with XmlDecoder, an attacker could exploit this to read sensitive files, access internal systems, or perform denial-of-service attacks by sending malicious XML payloads.

Compliance Impact

This vulnerability could lead to unauthorized data access or disclosure, violating GDPR's data protection principles or HIPAA's security requirements for protected health information. Organizations must patch to avoid compliance violations.

Mitigation Strategies

Update Netty to versions 4.1.136.Final or 4.2.16.Final or later to address the XML external entity risk in XmlDecoder.

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