CVE-2026-56745

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, the SpdyHttpDecoder handler in Netty's SPDY-to-HTTP codec allocates a pooled ByteBuf when processing a client-initiated SYN_STREAM frame with FLAG_FIN=0 and stores the partially constructed FullHttpRequest in messageMap; when the remote peer sends RST_STREAM for that stream or the accumulated content exceeds maxContentLength, the decoder removes the entry but does not release the pooled ByteBuf, causing native memory exhaustion. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

The SpdyHttpDecoder handler in Netty's SPDY-to-HTTP codec allocates a pooled ByteBuf when processing a client-initiated SYN_STREAM frame with FLAG_FIN=0, storing the partially-constructed FullHttpRequest in an internal map (messageMap) to accumulate subsequent DATA frames. When the remote peer sends an RST_STREAM for that stream, or when the accumulated content exceeds maxContentLength, the decoder removes the entry from the map but never releases the pooled ByteBuf, permanently leaking the allocated memory.

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-http 4.1.100.Final-rhlw-00001 with backported fixes for CVE-2024-29025, CVE-2025-58056, CVE-2025-67735, CVE-2026-33870, CVE-2026-41417, CVE-2026-42580, CVE-2026-42581, CVE-2026-42584, CVE-2026-42585, CVE-2026-42587, CVE-2026-50020, CVE-2026-55831, CVE-2026-55833, CVE-2026-56745, CVE-2026-56746, CVE-2026-59898, CVE-2026-59899, CVE-2026-59903, and CVE-2026-59921.

CVE-2024-29025: Netty HttpPostRequestDecoder can OOM

CVE-2025-58056: Netty is vulnerable to request smuggling due to incorrect parsing of chunk extensions

CVE-2025-67735: Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder

CVE-2026-33870: Netty: HTTP Request Smuggling via Chunked Extension Quoted-String Parsing

CVE-2026-41417: Netty vulnerable to HTTP request smuggling and RTSP request injection via DefaultHttpRequest.setUri()

CVE-2026-42580: Netty: HTTP Request Smuggling due to incorrect chunk size parsing

CVE-2026-42581: Netty: HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization

CVE-2026-42584: Netty: HttpClientCodec response desynchronization

CVE-2026-42585: Netty: HTTP Request Smuggling due to malformed Transfer-Encoding

CVE-2026-42587: Netty: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS

CVE-2026-50020: Netty's HttpObjectDecoder skips arbitrary initial control characters when only initial CRLF characters are permitted

CVE-2026-55831: Netty SPDY SETTINGS frame count materializes unbounded settings map

CVE-2026-55833: Netty SPDY zlib header block continues decoded expansion after maxHeaderSize truncation

CVE-2026-56745: Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion

CVE-2026-56746: Netty has a Security Control Bypass via CORS Short-Circuit Failure

CVE-2026-59898: Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation

CVE-2026-59899: Netty HttpContentEncoder: Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service

CVE-2026-59903: Netty: Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite

CVE-2026-59921: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

This patched artifact is a drop-in replacement for io.netty:netty-codec-http 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, the SpdyHttpDecoder handler in Netty's SPDY-to-HTTP codec allocates a pooled ByteBuf when processing a client-initiated SYN_STREAM frame with FLAG_FIN=0 and stores the partially constructed FullHttpRequest in messageMap; when the remote peer sends RST_STREAM for that stream or the accumulated content exceeds maxContentLength, the decoder removes the entry but does not release the pooled ByteBuf, causing native memory exhaustion. 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 14 io.netty packages to address 17 CVEs. Fixed in 4.2.12.Final-tuxcare.1.

TuxCare rebuilt 7 io.netty packages to address 12 CVEs. Fixed in 4.2.2.Final-tuxcare.2.

TuxCare rebuilt 8 io.netty packages to address 11 CVEs. Fixed in 4.1.114.Final-tuxcare.3.

TuxCare rebuilt 5 io.netty packages to address 9 CVEs. Fixed in 4.1.118.Final-tuxcare.2.

TuxCare rebuilt 3 io.netty packages to address 6 CVEs. Fixed in 4.1.113.Final-tuxcare.3.

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

Root has patched CVE-2026-56745 in the io.netty:netty-codec-http package for Root:Maven. Multiple fixed versions available.

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 +…