CVE-2026-56817

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.

Any caller that can deliver bytes to a Netty channel pipeline containing XmlDecoder can send XML with a DOCTYPE declaration to a parser instantiated with no security configuration — but whether external entities are actually resolved depends on Aalto XML's async parser behavior, making this a confirmed misconfiguration with conditional exploitability.

A client might overload the server by issue frequent RST frames. This can cause a massive amount of load on the remote system and so cause a DDOS attack.

Impact

This is a DDOS attack, any http2 server is affected and so you should update as soon as possible.

Patches

This is patched in version 4.1.100.Final.

Workarounds

A user can limit the amount of RST frames that are accepted per connection over a timeframe manually using either an own Http2FrameListener implementation or an ChannelInboundHandler implementation (depending which http2 API is used).

References

• https://www.cve.org/CVERecord?id=CVE-2023-44487
• https://blog.cloudflare.com/technical-breakdown-http2-rapid-reset-ddos-attack/
• https://cloud.google.com/blog/products/identity-security/google-cloud-mitigated-largest-ddos-attack-peaking-above-398-million-rps/

Red Hat Lightwell has released io.netty:netty-codec-xml 4.1.100.Final-rhlw-00001 with backported fixes for CVE-2026-56817 and CVE-2026-73507.

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

CVE-2026-73507: Netty: Denial of Service in XmlFrameDecoder via CPU Exhaustion

This patched artifact is a drop-in replacement for io.netty:netty-codec-xml 4.1.100.Final from Maven Central.

Root has patched GHSA-xpw8-rcwv-8f8p in the io.root.io.netty:netty-codec-http2 package for Root:Maven. Multiple fixed versions available.

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.

TuxCare rebuilt 47 io.netty packages to address 23 CVEs. Fixed in 4.1.135.Final-tuxcare.1.

TuxCare rebuilt 47 io.netty packages to address 23 CVEs. Fixed in 4.1.130.Final-tuxcare.3.

TuxCare rebuilt 47 io.netty packages to address 59 CVEs. Fixed in 4.1.122.Final-tuxcare.2.

TuxCare rebuilt 47 io.netty packages to address 60 CVEs. Fixed in 4.1.119.Final-tuxcare.1.

TuxCare rebuilt 47 io.netty packages to address 41 CVEs. Fixed in 4.1.112.Final-tuxcare.6.

TuxCare rebuilt 47 io.netty packages to address 62 CVEs. Fixed in 4.1.111.Final-tuxcare.1.

TuxCare rebuilt 47 io.netty packages to address 48 CVEs. Fixed in 4.1.117.Final-tuxcare.3.

TuxCare rebuilt 47 io.netty packages to address 61 CVEs. Fixed in 4.1.108.Final-tuxcare.1.

TuxCare rebuilt 47 io.netty packages to address 61 CVEs. Fixed in 4.1.107.Final-tuxcare.1.

TuxCare rebuilt 47 io.netty packages to address 62 CVEs. Fixed in 4.1.94.Final-tuxcare.1.

TuxCare rebuilt 47 io.netty packages to address 14 CVEs. Fixed in 4.1.115.Final-tuxcare.8.

TuxCare rebuilt 46 io.netty packages to address 22 CVEs. Fixed in 4.1.79.Final-tuxcare.4.

TuxCare rebuilt 8 io.netty packages to address 9 CVEs. Fixed in 4.1.93.Final-tuxcare.4.

TuxCare rebuilt 11 io.netty packages to address 18 CVEs. Fixed in 4.1.87.Final-tuxcare.1.

TuxCare rebuilt 9 io.netty packages to address 10 CVEs. Fixed in 4.1.92.Final-tuxcare.6.

TuxCare rebuilt 8 io.netty packages to address 17 CVEs. Fixed in 4.1.128.Final-tuxcare.1.

TuxCare rebuilt 13 io.netty packages to address 24 CVEs. Fixed in 4.1.114.Final-tuxcare.1.

TuxCare rebuilt 14 io.netty packages to address 17 CVEs. Fixed in 4.2.12.Final-tuxcare.1.

TuxCare rebuilt 10 io.netty packages to address 15 CVEs. Fixed in 4.1.113.Final-tuxcare.1.

TuxCare rebuilt 14 io.netty packages to address 16 CVEs. Fixed in 4.2.2.Final-tuxcare.1.

These are all security issues fixed in the netty-4.1.136-1.1 package on the GA media of openSUSE Tumbleweed.

This update for netty, netty-tcnative fixes the following issues:

Upgrade netty to upstream version 4.1.136 and netty-tcnative to version 2.0.80 Final.

Security issues fixed

• CVE-2026-44891: memory exhaustion in io.netty:netty-codec-stomp (bsc#1271435).
• CVE-2026-55831: resource exhaustion/DoS in io.netty:netty-codec-http (bsc#1271960).
• CVE-2026-55833: zip bomb in io.netty:netty-codec-http (bsc#1271961).
• CVE-2026-55851: memory exhaustion in io.netty:netty-codec-haproxy (bsc#1272253).
• CVE-2026-56745: memory exhaustion in io.netty:netty-codec-http (bsc#1272254).
• CVE-2026-56746: improper access control in io.netty:netty-codec-http (CORS) (bsc#1272255).
• CVE-2026-56817: insecure defaults in XML parsing in io.netty:netty-codec-xml (bsc#1272257).
• CVE-2026-56818: memory leak in io.netty:netty-codec-redis (bsc#1272603).
• CVE-2026-56819: memory leak in io.netty:netty-codec-http2 (bsc#1272258).
• CVE-2026-56820: improper certificate validation in io.netty:netty-handler-ssl-ocsp (bsc#1272259).
• CVE-2026-56821: improper certificate revocation check in io.netty:netty-handler-ssl-ocsp (bsc#1272299).
• CVE-2026-56822: time-of-check/time-of-use in io.netty:netty-handler-ssl-ocsp (bsc#1272300).
• CVE-2026-59898: protocol version confusion in io.netty:netty-codec-http (websocket) (bsc#1272302).
• CVE-2026-59899: memory exhaustion in io.netty:netty-codec-http (bsc#1272301).
• CVE-2026-59900: improper header neutralization in io.netty:netty-codec-http2 (bsc#1272303).
• CVE-2026-59901: infinite loop in io.netty:netty-codec-compression (bzip2) (bsc#1272304).
• CVE-2026-59919: improper CR/LF neutralization in io.netty:netty-codec-haproxy (bsc#1272305).
• CVE-2026-59920: improper CR/LF neutrolization in io.netty:netty-codec-stomp (bsc#1272306).
• CVE-2026-59921: improper CR/LF neutralization in io.netty:netty-codec-http (multipart) (bsc#1272307).
• Memory leak in io.netty:netty-codec-dns (bsc#1272519).
• Uncontrolled resource consumption in io.netty:netty-codec-xml (bsc#1272518).

Other updates and bugfixes:

• Upgrade to upstream version 4.1.136:
  • SingleThreadEventExecutor: document Throwable safety contract on run()
  • Make HTTP/2 frame hashCode consistent with equals
  • Add BlockHound exception for DnsQueryIdSpace (#16896)
  • FlowControlHandler: Fix autoRead behavior
  • Fix incorrect bounds in error message of HpackDecoder.setMaxHeaderListSize
  • MQTT: Fix MQTT decoder size check after variable header replay
  • MQTT: Make the decodeProperties early-REPLAY check actually fire
  • Reject control characters at the boundary of HTTP method names (#16723)
  • Update to latest tcnative release
  • Fix HTTP 2 PUSH_PROMISE stream association validation
  • Fix GZIP FEXTRA extra-field handling in JdkZlibDecoder
  • Add opt-in validation of mandatory pseudo-header fields for HTTP/2
  • Strictly validate MQTT UTF-8 Encoded String (#16939)
  • Stop DateFormatter trailing token from running past the parse end
  • IpFilter: Deprecate constructor which use accept by default
  • Add RFC 10008 QUERY Method support (#16966)
  • Correctly release and fail queued traffic-shaping writes on close (#16959)
  • FlowControlHandler: respect auto-read when toggled while dequeueing
  • IdleStateHandler: reset firstWriter/ReaderIdleEvent in resetWriteTimeout/resetReadTimeout (#16982)
  • Fix typo in AbstractSniHandler Javadoc
  • Reconcile AbstractCoalescingBufferQueue readableBytes when it drains, and fail stuck HTTP/2 streams instead of spinning empty DATA frames
  • Reject control characters at the boundary of the HTTP version token (#16971)
  • Reset UTF-8 decode state on CR in StompSubframeDecoder
  • HTTP2: Pass the correct number of arguments when logging goaway
  • FastLz: Guard decompression against truncated input (#17000)
  • Fix propagation of startTls for client SslContext handler
  • Reject non-token characters in HTTP/2 header names +…