CVE-2026-42583 Netty: Lz4FrameDecoder resource exhaustion
Attackers can cause resource exhaustion in Netty's Lz4FrameDecoder by sending small payloads that trigger large memory allocations, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42583?
CVE-2026-42583 is a high-severity denial of service vulnerability in Netty Netty, published on 13 May 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 4.2.13.Final and 4.1.133.Final, Lz4FrameDecoder allocates a ByteBuf of size decompressedLength (up to 32 MB per block) before LZ4 runs. A peer only needs a 21-byte header plus compressedLength payload bytes - 22 bytes if compressedLength == 1 - to force that allocation. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Which versions are affected by CVE-2026-42583?
4 open source packages ship an affected version, including io.netty:netty-codec and io.netty:netty-codec-compression. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-codec Maven | All versions | 4.1.133.Final |
io.netty:netty-codec Maven | All versions | 4.1.133.Final |
io.netty:netty-codec-compression Maven | All versions | 4.2.13.Final |
io.netty:netty-codec-compression Maven | All versions | 4.2.13.Final |
Products include Netty Netty.
How do I fix CVE-2026-42583?
Upgrade io.netty:netty-codec to 4.1.133.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-2026-42583 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42583 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-FA85368, CLEANSTART-2026-FP82534, CLEANSTART-2026-GG28030, CLEANSTART-2026-HW56011, CLEANSTART-2026-LU91275, CLEANSTART-2026-RZ47528 and 116 more.