CVE-2026-42584 Netty: HttpClientCodec response desynchronization
Netty's HttpClientCodec mishandles 1xx responses, causing response desynchronization and potential data leakage or parsing errors in pipelined requests.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42584?
CVE-2026-42584 is a high-severity vulnerability in Netty Netty, published on 13 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Weakness: CWE-444
Which versions are affected by CVE-2026-42584?
4 open source packages ship an affected version, including io.netty:netty-codec-http. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec-http Maven | All versions | 4.1.133.Final |
io.netty:netty-codec-http Maven | All versions | 4.1.133.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Alpha1 | 4.2.13.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Alpha1 | 4.2.13.Final |
Products include Netty Netty.
How do I fix CVE-2026-42584?
Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.133.Final or 4.2.13.Final.
Is CVE-2026-42584 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42584 exists.
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-BW02780, CLEANSTART-2026-FU44475, CLEANSTART-2026-OB06695, CLEANSTART-2026-OX18786, CLEANSTART-2026-SS19101, CLEANSTART-2026-UB69946 and 104 more.