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Intro: How CVE-2026-44890 Works
This vulnerability lies in Netty’s RedisDecoder, a component used to parse the Redis Serialization Protocol (RESP) for applications that communicate directly with a Redis server without a separate proxy. The core issue is an uncontrolled resource consumption flaw in the `decodeLength` method when handling malformed RESP data.
According to the RESP specification, all protocol elements—including the length prefix of a bulk string ($) or array (“)—must be strictly terminated by a `\r\n` sequence. The `decodeLength` method reads bytes from the incoming network stream until it finds a newline character (\n). However, in versions prior to the fix, this method does not enforce any maximum length or timeout while buffering these bytes if the terminating `\n` is not found.
An attacker can exploit this by opening multiple concurrent connections to the target server. On each connection, they send a continuous stream of numeric digits intended to represent the length of a bulk string (e.g., $1111...). Critically, the attacker deliberately omits the required terminating `\n` character. The `decodeLength` method will then begin buffering this stream of digits in memory, waiting indefinitely for the terminator.
Because there is no bound on the length of this digit stream, an attacker sending payloads like `$9999999999…` across many connections will cause the decoder to allocate an unbounded amount of direct memory. This leads to resource exhaustion, ultimately triggering an `OutOfDirectMemoryError` and preventing the server from processing legitimate connection requests, resulting in a complete Denial of Service (DoS).
The fix, included in Netty `4.2.15.Final` and 4.1.135.Final, implements a maximum length limit for this digit stream, rejecting and closing connections that violate the protocol immediately, thus preventing the unbounded memory allocation.
DailyCVE Form
Platform: Netty
Version: ≤4.2.14.Final; ≤4.1.134.Final
Vulnerability : Unbounded Direct Memory
Severity: High
date: 2026-06-08
Prediction: 2026-06-02
What Undercode Say
Vulnerability Analytics
$ echo "Netty versions before 4.2.15.Final and 4.1.135.Final" $ echo "Affected module: netty-codec-redis" $ echo "CWE-400: Uncontrolled Resource Consumption" $ echo "CVE-2026-44890 severity: High" $ echo "Attack vector: Remote" $ echo "Attack complexity: Low" $ echo "No public exploit as of June 8, 2026"
Exploit:
To trigger the vulnerability, an attacker would open multiple connections to the target Netty-based service. On each connection, they would send a crafted RESP bulk string header without the terminating `\r\n` sequence.
Conceptual Payload (never terminates):
1\r\n$99999999999999999999
The critical aspect is that the numeric sequence after `$` is infinite or extremely long, and is not followed by \r\n. The `RedisDecoder` will buffer this indefinitely, exhausting direct memory.
Protection:
Immediate Upgrade: Update the `netty-codec-redis` library to patched versions 4.2.15.Final or 4.1.135.Final, which include a limit on the length of the digit stream.
Network Mitigation: Deploy a reverse proxy or firewall that can inspect and block malformed RESP traffic missing required `\r\n` terminators.
Memory Limits: Enforce and monitor direct memory limits (-Dio.netty.maxDirectMemory), although this is a mitigation, not a fix.
Impact:
Successful exploitation leads to a complete Denial of Service due to memory exhaustion (OutOfDirectMemoryError). Any application that uses Netty’s `RedisDecoder` to parse untrusted or external Redis protocol data is vulnerable, including custom Redis proxies, monitoring tools, and applications embedding a Redis protocol gateway.
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Sources:
Reported By: github.com
Extra Source Hub:
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