Hello, fellow Plex enthusiasts and security-minded users! Today, we will be diving into CVE-2021-33959, a serious vulnerability affecting Plex Media Server versions 1.21 and earlier. This vulnerability allows attackers to perform a Distributed Denial of Service (DDoS) reflection attack using the Plex service. In this post, we'll explore what this vulnerability is, how it can be exploited, and what you can do to protect your Plex Media Server.

The Vulnerability - CVE-2021-33959

CVE-2021-33959 is a vulnerability identified in Plex Media Server versions 1.21 and earlier, which could potentially allow for DDoS reflection attacks. More specifically, this vulnerability exists due to the Plex service's improper handling of multicast packets, which can be used by an attacker to amplify a DDoS attack.

Here is an example of the code snippet causing the vulnerability

def handle_multicast_packet(packet):
    if not packet.is_valid():
        return
    if packet.sender == self._get_server_address():
        return
    response = create_amplified_response(packet)
    self._send_packet(response)

The above function does not properly validate the source of incoming multicast packets, which can be exploited by attackers to create amplified responses, magnifying the impact of a DDoS attack.

The Attack - A DDoS Reflection

A DDoS reflection attack occurs when an attacker sends a large number of requests to various services, using a spoofed source IP address belonging to the actual target of the attack. In this case, the Plex service is used to create amplified responses directing traffic to that target.

The attacker crafts malicious packets, which are then picked up by the vulnerable Plex service. Due to the lack of proper validation in the code snippet shown earlier, these packets then create amplified responses, flooding the target IP address with traffic and overwhelming their network resources.

1. CVE-2021-33959 at Rapid7.com
2. PLEX Media Server at Mitre.org

To protect your Plex Media Server from this vulnerability, you should take the following steps

1. Update Plex Media Server: If you are running Plex Media Server version 1.21 or earlier, update to the latest version immediately. Plex has released a patch for this vulnerability, so updating your software is crucial for staying safe.

2. Block Unnecessary Incoming Traffic: Configure your firewall to restrict incoming traffic to your Plex Media Server. Most home networks should only allow authorized devices to connect to your server. This will prevent attackers from sending malicious packets to your server in the first place.

3. Monitor Network Activity: Keep an eye on your server's network activity, looking out for any unusual bandwidth usage or irregular traffic patterns. This can help you detect and react to potential DDoS attacks before they do significant damage.

In conclusion, CVE-2021-33959 poses a significant security risk to Plex Media Server users, enabling attackers to perform DDoS reflection attacks. By updating your Plex Media Server and following the recommended security precautions, you can ensure your media streaming experience remains safe and enjoyable!

Timeline

Published on: 01/18/2023 14:15:00 UTC
Last modified on: 01/26/2023 16:15:00 UTC