CVE-2026-42585 Netty: HTTP Request Smuggling due to malformed Transfer-Encoding
Attackers can exploit malformed Transfer-Encoding headers to smuggle HTTP requests, bypassing security controls and potentially accessing sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42585?
CVE-2026-42585 is a medium-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, Netty incorrectly parses malformed Transfer-Encoding, enabling request smuggling attacks. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Weakness: CWE-444
Which versions are affected by CVE-2026-42585?
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-2026-42585?
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-2026-42585 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42585 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-MO89596, CLEANSTART-2026-PE62023, CLEANSTART-2026-QH29920, CLEANSTART-2026-YF85147, CLEANSTART-2026-ZP44321, DEBIAN-CVE-2026-42585 and 98 more.