CVE-2026-56817 Netty: XML External Entity (XXE) injection via unconfigured XML factory when DTD and entity processing are enabled
Attackers can exploit XML External Entity vulnerabilities in Netty's XmlDecoder if DTD processing is enabled, potentially reading files or causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-56817?
CVE-2026-56817 is a high-severity vulnerability in Netty Netty, published on 21 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-611
Which versions are affected by CVE-2026-56817?
4 open source packages ship an affected version, including io.netty:netty-codec-xml. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec-xml Maven | From 4.1.0.Final | 4.1.136.Final |
io.netty:netty-codec-xml Maven | From 4.1.0.Final | 4.1.136.Final |
io.netty:netty-codec-xml Maven | From 4.2.0.Final | 4.2.16.Final |
io.netty:netty-codec-xml Maven | From 4.2.0.Final | 4.2.16.Final |
Products include Netty Netty.
How do I fix CVE-2026-56817?
Upgrade io.netty:netty-codec-xml to a fixed version for your release line: 4.1.136.Final or 4.2.16.Final.
Is CVE-2026-56817 being exploited?
There is no known exploitation of CVE-2026-56817 in the wild and no public exploit code.
Other vulnerabilities in Netty Netty
- CVE-2026-75595 Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- CVE-2026-75596 Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- CVE-2026-59901 Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
- CVE-2026-55851 Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
- CVE-2026-56745 Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
Sources
Also known as CLEANSTART-2026-LD69815, CLEANSTART-2026-TT58644, DEBIAN-CVE-2026-56817, GHSA-4qhr-g3c6-fcfx, MINI-6836-qr6v-5h8g, MINI-77v4-wpr8-2mmj and 9 more.