CVE-2026-33870 Netty: HTTP Request Smuggling via Chunked Extension Quoted-String Parsing
Attackers can perform HTTP request smuggling by exploiting incorrect parsing of chunked extension quoted strings in Netty.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33870?
CVE-2026-33870 is a high-severity vulnerability in Netty Netty, published on 27 Mar 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. In versions prior to 4.1.132.Final and 4.2.10.Final, Netty incorrectly parses quoted strings in HTTP/1.1 chunked transfer encoding extension values, enabling request smuggling attacks. Versions 4.1.132.Final and 4.2.10.Final fix the issue.
Weakness: CWE-444
Which versions are affected by CVE-2026-33870?
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 | 4.1.132.Final |
io.netty:netty-codec-http Maven | All versions | 4.1.132.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Alpha1 | 4.2.10.Final |
io.netty:netty-codec-http Maven | From 4.2.0.Alpha1 | 4.2.10.Final |
Products include Netty Netty.
How do I fix CVE-2026-33870?
Upgrade io.netty:netty-codec-http to a fixed version for your release line: 4.1.132.Final or 4.2.10.Final.
Is CVE-2026-33870 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33870 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-DF15314, CLEANSTART-2026-LA46577, CLEANSTART-2026-PC14527, CLEANSTART-2026-WZ23754, CLSA-2026-1793127400, DEBIAN-CVE-2026-33870 and 80 more.