CVE-2026-59898 Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation
Attackers can bypass proxy security checks and enable HTTP request smuggling by exploiting missing header validation in Netty's WebSocket handshaker.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59898?
CVE-2026-59898 is a medium-severity vulnerability in Netty Netty, published on 29 Jul 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 versions 4.1.136.Final and 4.2.16.Final, ab attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending `Sec-WebSocket-Version: 7` and omitting `Connection: Upgrade` / `Upgrade: websocket` headers, completing a protocol switch that a proxy would not recognize as an Upgrade request and enabling HTTP request smuggling / protocol-confusion attacks. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.
Weakness: CWE-444
Which versions are affected by CVE-2026-59898?
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 | 4.1.136.Final |
io.netty:netty-codec-http Maven | All versions | 4.1.136.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Final | 4.2.16.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Final | 4.2.16.Final |
Products include Netty Netty.
How do I fix CVE-2026-59898?
Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.136.Final or 4.2.16.Final.
Is CVE-2026-59898 being exploited?
There is no known exploitation of CVE-2026-59898 in the wild and no public exploit code.
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-AP50361, CLEANSTART-2026-HQ95563, CLEANSTART-2026-JC38866, CLEANSTART-2026-SM18650, CLEANSTART-2026-WY62570, DEBIAN-CVE-2026-59898 and 108 more.