Security Vulnerability Report: CRLF Injection in Netty Redis Codec Encoder

1. Vulnerability Summary

| Field | Value | |-------|-------| | Product | Netty | | Version | 4.2.12.Final (and all prior versions with codec-redis) | | Component | io.netty.handler.codec.redis.RedisEncoder | | Vulnerability Type | CWE-93: Improper Neutralization of CRLF Sequences (CRLF Injection) | | Impact | Redis Command Injection / Response Poisoning | | Attack Vector | Network | | Attack Complexity | Low | | Privileges Required | None | | User Interaction | None | | Scope | Unchanged | | Confidentiality Impact | High | | Integrity Impact | High | | Availability Impact | None |

2. Affected Components

The following classes in the codec-redis module are affected:

• io.netty.handler.codec.redis.RedisEncoder (encoder - no output validation)
• io.netty.handler.codec.redis.InlineCommandRedisMessage (no input validation)
• io.netty.handler.codec.redis.SimpleStringRedisMessage (no input validation)
• io.netty.handler.codec.redis.ErrorRedisMessage (no input validation)
• io.netty.handler.codec.redis.AbstractStringRedisMessage (base class - no validation)

3. Vulnerability Description

The Netty Redis codec encoder (RedisEncoder) writes user-controlled string content directly to the network output buffer without validating or sanitizing CRLF (\r\n) characters. Since the Redis Serialization Protocol (RESP) uses CRLF as the command/response delimiter, an attacker who can control the content of a Redis message can inject arbitrary Redis commands or forge fake responses.

Root Cause

In RedisEncoder.java, the writeString() method (lines 103-111) writes content using ByteBufUtil.writeUtf8() without any validation:

private static void writeString(ByteBufAllocator allocator, RedisMessageType type,
                                String content, List<Object> out) {
    ByteBuf buf =...