CVE-2026-56816 Netty: Memory Exhaustion via HTTP/3 Reserved Frame Types
An attacker can cause memory exhaustion and denial of service in Netty by sending HTTP/3 reserved frames with large payload lengths.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-56816?
CVE-2026-56816 is a high-severity denial of service vulnerability in Netty Netty, published on 21 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Netty is a network application framework for development of protocol servers and clients. Prior to 4.2.16.Final, Netty's `Http3FrameCodec` buffers incoming data for HTTP/3 reserved frame types up to the wire-specified payload length without limits; `decodeFrame` trusts `payLoadLength`, allowing an attacker to open multiple QUIC streams and send reserved frames with very large payload lengths to cause memory exhaustion and denial of service. This issue is fixed in version 4.2.16.Final.
Weakness: CWE-400
Which versions are affected by CVE-2026-56816?
2 open source packages ship an affected version, including io.netty:netty-codec-http3. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec-http3 Maven | All versions | 4.2.16.Final |
io.netty:netty-codec-http3 Maven | All versions | 4.2.16.Final |
Products include Netty Netty.
How do I fix CVE-2026-56816?
Upgrade io.netty:netty-codec-http3 to 4.2.16.Final or later.
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-2026-56816 being exploited?
There is no known exploitation of CVE-2026-56816 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-ET24110, CLEANSTART-2026-NR68186, DEBIAN-CVE-2026-56816, ECHO-d208-62e1-f7a7, GHSA-hpcc-26xq-25fv, MINI-2hvq-2mxv-6c6j and 10 more.