CVE-2026-56819 Netty: HTTP/2 decompression leaks ByteBuf reference count when the decompressor channel is already closed (Direct memory leak / OOM DoS)
Remote attackers can cause a denial of service by exhausting direct memory in Netty applications using HTTP/2 decompression.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-56819?
CVE-2026-56819 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. In versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, a remote unauthenticated peer can leak one direct `ByteBuf` per HTTP/2 `DATA` frame in applications that enable HTTP/2 content decompression via `DelegatingDecompressorFrameListener`. When a `DATA` frame is processed for a stream whose decompressor has already been closed, `Http2Decompressor.decompress(...)` calls `decompressor.writeInbound(data.retain())` and does not release the retained buffer on the error path, eventually exhausting direct memory and crashing the JVM. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.
Which versions are affected by CVE-2026-56819?
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 | From 4.1.0.Final | 4.1.136.Final |
io.netty:netty-codec-http2 Maven | From 4.1.0.Final | 4.1.136.Final |
io.netty:netty-codec-http2 Maven | From 4.2.0 | 4.2.16.Final |
io.netty:netty-codec-http2 Maven | From 4.2.0 | 4.2.16.Final |
Products include Netty Netty.
How do I fix CVE-2026-56819?
Upgrade io.netty:netty-codec-http2 to a fixed version for your release line: 4.1.136.Final or 4.2.16.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-2026-56819 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56819 exists.
Public exploit code: 1 proofs of concept on GitHub.
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-CP47219, CLEANSTART-2026-DG55776, CLEANSTART-2026-PW77376, CLEANSTART-2026-TY09465, DEBIAN-CVE-2026-56819, ECHO-7258-9374-4a42 and 89 more.