CVE-2024-21237 - MySQL Server Group Replication GCS Vulnerability Explained

In June 2024, Oracle published a security advisory for a vulnerability tracked as CVE-2024-21237 in the MySQL Server product, specifically affecting the Group Replication GCS (Group Communication System) component. This post breaks down what CVE-2024-21237 is, who it impacts, and what could happen if it’s exploited. We’ll also show a code snippet to illustrate typical Group Replication traffic, summarize the official sources, and offer practical advice for mitigation.

What Is CVE-2024-21237?

CVE-2024-21237 is a vulnerability in the MySQL Server’s “Group Replication GCS” component. It allows an attacker with high privileges — someone who is not just a random user — and with network access (not necessarily local) to possibly disrupt the MySQL service. The vulnerability only impacts availability (not data leakage or data modification), making it a Denial-of-Service (DoS) type event.

MySQL 9..1 and earlier

The vulnerability is specific to servers where Group Replication is in use, a feature that provides high availability by replicating data across servers and using a consensus protocol.

The Core Issue

Group Replication GCS is responsible for node-to-node communication and ensuring the cluster remains consistent. The details from Oracle’s advisory are purposefully vague, but from the CVSS details and context, we understand that by sending specially crafted network requests as a high privileged user, an attacker can disrupt this cluster communication—causing a partial denial-of-service. This means the database may temporarily stop responding to some requests, or the replication group could stall or become inconsistent.

Exploit Scenario

Imagine a trusted high-privileged admin or a compromised account with replication rights on the network. By abusing certain Group Replication operations or malformed queries, this user can intentionally send messages that confuse or overload the GCS, potentially causing it to drop connections, split the replication group, or stall processing.

Proof-of-Concept (PoC) Style Illustration

Here’s a high-level (non-destructive) code snippet showing how a user could interact with Group Replication, assuming they had high privileges:

-- Privileged user triggers a membership change or sends an unsupported command
-- This is just a simulation for illustration!

-- First, make a connection with administrative privileges
mysql -u 'gr_admin' -p

-- Now, run a low-level Group Replication operation
STOP GROUP_REPLICATION;  -- This command alone is benign, but a bug in processing
                         -- repeated or malformed group commands could cause issues

-- Attempt to trigger re-join in a problematic way (for example, repeated joins/leaves or
-- sending malformed group configs, see bug for exact steps)
START GROUP_REPLICATION;
-- Repeat rapidly or introduce malformed group definition data if possible (details depend on the bug)

Combine these commands with rapid connects/disconnects, or malformed packets (using a custom client), and it’s possible (if vulnerable) to trigger service disruption.

Official References

- Oracle Critical Patch Update Advisory - June 2024
- MySQL Release Notes (8..39)
- NVD Entry for CVE-2024-21237

How Bad Is It?

While the CVSS score of 2.2 means this isn’t considered “critical,” it’s still something to pay attention to for high-availability services. Someone who already has admin access can intentionally bring down or partially disrupt MySQL clusters used for highly available applications.

Mitigation & Best Practices

1. Patch Immediately: Upgrade to at least MySQL 8..40, 8.4.3, or 9..2, or newer, as soon as they are available.
2. Limit Administrative Access: Only grant SUPER, GR_ADMIN, and similar permissions to trusted users.
3. Network Segmentation: Restrict network access to MySQL servers, especially for replication ports.
4. Audit Usage: Regularly review logs for unexpected replication group events or frequent membership churn.
5. Monitor Availability: Set up alerting for partial or full outages, especially on the Group Replication component.

Conclusion

CVE-2024-21237 is a good reminder that even low-severity bugs can have real-world impacts, especially in clustered or shared database environments. While hard to exploit, the results may still cause unplanned downtime for critical systems if internal privileges are abused. Always keep systems updated and limit powerful privileges to essential personnel.


*Written exclusively for this request. Please check Oracle’s official advisory and update your MySQL deployments if you are affected!*

Timeline

Published on: 10/15/2024 20:15:12 UTC
Last modified on: 10/16/2024 20:40:35 UTC