Vulnerability · Published Jul 21, 2026 · Assigned by GitHub_M

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

High 8.3

In plain English

A high-severity XML external entity in netty from netty. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 53% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.3High

Exploit odds (30 days)0.7%top 46.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	netty	no fix listed	DEBIAN-CVE-2026-56817
Debian:13	netty	no fix listed	DEBIAN-CVE-2026-56817
Debian:14	netty	no fix listed	DEBIAN-CVE-2026-56817
Maven	io.netty:netty-codec-xml	4.2.16.Final	GHSA-4qhr-g3c6-fcfx
Maven	io.netty:netty-codec-xml	4.1.136.Final	GHSA-4qhr-g3c6-fcfx
Ubuntu:26.10	netty	no fix listed	UBUNTU-CVE-2026-56817

Affected products (as reported)

Vendor	Product	Versions
netty	netty	>= 4.2.0.Final, < 4.2.16.Final>= 4.1.0.Final, < 4.1.136.Final

Weakness: CWE-611 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N

References

https://github.com/netty/netty/security/advisories/GHSA-4qhr-g3c6-fcfx x_refsource_CONFIRM
https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b x_refsource_MISC
https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6 x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final x_refsource_MISC