Executive brief
Netty is a widely used networking framework for Java applications. A vulnerability in its XML processing component could allow an attacker to send specially crafted XML messages that trick the system into accessing unauthorized files or internal network resources. This could lead to the exposure of sensitive data or impact the availability of the service.
Technical details
An Improper Restriction of XML External Entity Reference (XXE) vulnerability exists in Netty's `netty-codec-xml` module. The `XmlDecoder` component utilizes an `AsyncXMLInputFactory` (often backed by Aalto XML) that is instantiated without disabling DTDs or external entity resolution. A remote, unauthenticated attacker can exploit this by sending XML containing a `DOCTYPE` declaration to a Netty channel pipeline. Successful exploitation could lead to local file disclosure or server-side request forgery (SSRF), though actual exploitability may depend on the specific behavior of the underlying asynchronous parser. The issue is resolved in versions 4.1.136.Final and 4.2.16.Final.
Affected products
- Netty netty-codec-xml >= 4.1.0.Final, <= 4.1.135.Final
- Netty netty-codec-xml >= 4.2.0.Final, <= 4.2.15.Final
Timeline
- 2026-07-14: disclosed: Initial disclosure by maintainers
- 2026-07-21: advisory: NVD publication date
- 2026-07-22: patched: GitHub Advisory reviewed and updated with patch information
References
- https://github.com/netty/netty/security/advisories/GHSA-4qhr-g3c6-fcfx
- https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b
- https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6
- https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
- https://github.com/netty/netty/releases/tag/netty-4.2.16.Final