CVE-2026-44248

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, the MQTT 5 header Properties section is parsed and buffered before any message size limit is applied. Specifically, in MqttDecoder, the decodeVariableHeader() method is called before the bytesRemainingBeforeVariableHeader > maxBytesInMessage check. The decodeVariableHeader() can call other methods which will call decodeProperties(). Effectively, Netty does not apply any limits to the size of the properties being decoded. Additionally, because MqttDecoder extends ReplayingDecoder, Netty will repeatedly re-parse the enormous Properties sections and buffer the bytes in memory, until the entire thing parses to completion. This can cause high resource usage in both CPU and memory. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Impact

The MQTT 5 header Properties section is parsed and buffered before any message size limit is applied.

Specifically, in MqttDecoder, the decodeVariableHeader() method is called before the bytesRemainingBeforeVariableHeader > maxBytesInMessage check. The decodeVariableHeader() can call other methods which will call decodeProperties(). Effectively, Netty does not apply any limits to the size of the properties being decoded.

Additionally, because MqttDecoder extends ReplayingDecoder, Netty will repeatedly re-parse the enormous Properties sections and buffer the bytes in memory, until the entire thing parses to completion.

This can cause high resource usage in both CPU and memory.

Resources

ANT-2026-09608 https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901027

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-mqtt 4.1.100.Final-rhlw-00001 with a backported security fix.

CVE-2026-44248: Netty: Resource exhaustion in MqttDecoder

This patched artifact is a drop-in replacement for io.netty:netty-codec-mqtt 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 an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, the MQTT 5 header Properties section is parsed and buffered before any message size limit is applied. Specifically, in MqttDecoder, the decodeVariableHeader() method is called before the bytesRemainingBeforeVariableHeader > maxBytesInMessage check. The decodeVariableHeader() can call other methods which will call decodeProperties(). Effectively, Netty does not apply any limits to the size of the properties being decoded. Additionally, because MqttDecoder extends ReplayingDecoder, Netty will repeatedly re-parse the enormous Properties sections and buffer the bytes in memory, until the entire thing parses to completion. This can cause high resource usage in both CPU and memory. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

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 6 io.netty packages to address 6 CVEs. Fixed in 4.1.130.Final-tuxcare.4.

TuxCare rebuilt 12 io.netty packages to address 28 CVEs. Fixed in 4.1.79.Final-tuxcare.2.

TuxCare rebuilt 12 io.netty packages to address 19 CVEs. Fixed in 4.1.75.Final-tuxcare.5.

TuxCare rebuilt 43 io.netty packages to address 7 CVEs. Fixed in 4.1.63.Final-tuxcare.8.

TuxCare rebuilt 11 io.netty packages to address 20 CVEs. Fixed in 4.1.73.Final-tuxcare.5.

TuxCare rebuilt 47 io.netty packages to address 19 CVEs. Fixed in 4.1.99.Final-tuxcare.1.

TuxCare rebuilt 5 io.netty packages to address 9 CVEs. Fixed in 4.1.48.Final-tuxcare.4.

TuxCare rebuilt 47 io.netty packages to address 19 CVEs. Fixed in 4.1.96.Final-tuxcare.1.

TuxCare rebuilt 15 io.netty packages to address 27 CVEs. Fixed in 4.1.72.Final-tuxcare.1.

TuxCare rebuilt 43 io.netty packages to address 25 CVEs. Fixed in 4.1.68.Final-tuxcare.1.

TuxCare rebuilt 14 io.netty packages to address 26 CVEs. Fixed in 4.1.118.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 40 io.netty packages to address 26 CVEs. Fixed in 4.1.53.Final-tuxcare.1.

TuxCare rebuilt 7 io.netty packages to address 8 CVEs. Fixed in 4.1.52.Final-tuxcare.4.

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

TuxCare rebuilt 13 io.netty packages to address 24 CVEs. Fixed in 4.1.74.Final-tuxcare.1.

TuxCare rebuilt 10 io.netty packages to address 17 CVEs. Fixed in 4.1.49.Final-tuxcare.6.

TuxCare rebuilt 8 io.netty packages to address 12 CVEs. Fixed in 4.1.101.Final-tuxcare.2.

TuxCare rebuilt 5 io.netty packages to address 4 CVEs. Fixed in 4.1.128.Final-tuxcare.3.

TuxCare rebuilt 6 io.netty packages to address 10 CVEs. Fixed in 4.1.100.Final-tuxcare.2.

TuxCare rebuilt 43 io.netty packages to address 22 CVEs. Fixed in 4.1.60.Final-tuxcare.3.

TuxCare rebuilt 14 io.netty packages to address 32 CVEs. Fixed in 4.1.64.Final-tuxcare.1.

These are all security issues fixed in the netty-4.1.133-1.1 package on the GA media of openSUSE Tumbleweed.

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

• CVE-2026-41417: missing validations leads to HTTP request smuggling and RTSP request injection via start-line injection in DefaultHttpRequest.setUri() (bsc#1264350).
• CVE-2026-42578: HTTP Header Injection via HttpProxyHandler Disabled Validation in Netty (bsc#1265243).
• CVE-2026-42579: DNS codec does not enforce RFC 1035 domain name constraints during either encoding or decoding (bsc#1265272).
• CVE-2026-42580: chunk size parser silently overflows int and enables request smuggling attacks (bsc#1265273).
• CVE-2026-42581: TE+CL header coexistence in HTTP/1.0 requests bypasses smuggling sanitization (bsc#1265277).
• CVE-2026-42583: resource exhaustion and possible denial of service via Lz4FrameDecoder (bsc#1265279).
• CVE-2026-42584: improper handling of inbound responses in HttpClientCodec can lead to response desynchronization (bsc#1265280).
• CVE-2026-42585: Netty is an asynchronous, event-driven network application framework (bsc#1265292).
• CVE-2026-42586: CRLF Injection in Netty Redis Codec Encoder (bsc#1265245).
• CVE-2026-42587: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS (bsc#1265246).
• CVE-2026-44248: Netty is an asynchronous, event-driven network application framework (bsc#1265294).
• CVE-2026-42582: HTTP/3 QPACK literal unbounded allocation (bsc#1265318).

Changes for netty:

• Upgrade to upstream version 4.1.133