CVE-2026-33871 Netty HTTP/2 CONTINUATION Frame Flood DoS via Zero-Byte Frame Bypass
Remote attackers can cause Denial of Service in Netty HTTP/2 servers by flooding zero-byte CONTINUATION frames, bypassing size limits and exhausting CPU resources.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33871?
CVE-2026-33871 is a high-severity denial of service 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, a remote user can trigger a Denial of Service (DoS) against a Netty HTTP/2 server by sending a flood of `CONTINUATION` frames. The server's lack of a limit on the number of `CONTINUATION` frames, combined with a bypass of existing size-based mitigations using zero-byte frames, allows an user to cause excessive CPU consumption with minimal bandwidth, rendering the server unresponsive. Versions 4.1.132.Final and 4.2.10.Final fix the issue.
Weakness: CWE-770
Which versions are affected by CVE-2026-33871?
4 open source packages ship an affected version, including io.netty:netty-codec-http2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec-http2 Maven | All versions | 4.1.132.Final |
io.netty:netty-codec-http2 Maven | All versions | 4.1.132.Final |
io.netty:netty-codec-http2 Maven | From 4.2.0.Alpha1 | 4.2.11.Final |
io.netty:netty-codec-http2 Maven | From 4.2.0.Alpha1 | 4.2.11.Final |
Products include Netty Netty.
How do I fix CVE-2026-33871?
Upgrade io.netty:netty-codec-http2 to a fixed version for your release line: 4.1.132.Final or 4.2.11.Final.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-33871 being exploited?
There is no known exploitation of CVE-2026-33871 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-EW06968, CLEANSTART-2026-FG87106, CLEANSTART-2026-RX34161, DEBIAN-CVE-2026-33871, ECHO-bdd6-9d7a-9895, GHSA-w9fj-cfpg-grvv and 65 more.