CVE-2026-57216 is a medium severity (CVSS 6.8) authentication flaw in RabbitMQ. A loopback restricted user such as guest can connect remotely when traffic arrives through a trusted PROXY protocol path. Fixed in 3.13.15, 4.0.20, 4.1.11 and 4.2.6. Delete the guest user if you do not need it.
What's affected
The RabbitMQ advisory (GHSA-36m6-588r-vqcw) lists four affected branches. Fixed versions: 4.2.6 for 4.2.0 up to 4.2.6, 4.1.11 for 4.1.0 up to 4.1.11, 4.0.20 for 4.0.0 up to 4.0.20, and 3.13.15 for 3.13.0 up to 3.13.15.
The condition is specific. The broker must accept traffic through a trusted PROXY protocol path, and its listener must be bound to loopback. The check that limits a user like guest to local connections used the listener side address rather than the real client address. So the check saw a loopback address and allowed a connection that came from elsewhere.
The advisory covers AMQP 0-9-1, AMQP 1.0 and the Stream protocol.
How to check if you're exposed
rabbitmqctl version
rabbitmqctl list_users
- Compare the version with the fixed versions above.
- Check whether you use the PROXY protocol on listeners behind a load balancer or proxy.
- Check whether the guest user still exists with its default password. If it does, delete it or change the password.
Run the free in-browser dependency scan at https://gold.safeguard.sh/scan against your manifest or lockfile. It lists vulnerable packages without installing anything.
What to do now
- Upgrade to 4.2.6, 4.1.11, 4.0.20 or 3.13.15, depending on your branch.
- Delete the guest user if you do not need it, or at least change its password.
- Create named users with their own permissions for each application.
- Only accept PROXY protocol from proxies you control, and firewall the broker so clients cannot reach it directly.
- Review connection logs for the guest user from non-local peers.
Why it matters
The weakness is CWE-287, improper authentication. A rule meant to say a user may only connect from this machine was evaluated against the wrong address. Behind a proxy, the address of the socket is the proxy's local one, while the real client is elsewhere, so the rule passed when it should have failed.
The wider point is that default accounts exist to make first start easy and should not survive into production. The vector shows high complexity, since it needs a particular proxy setup. The record is not in CISA's Known Exploited Vulnerabilities catalog.
Quick check
Do I need the PROXY protocol for the flaw to matter?
Yes. The advisory ties the flaw to traffic accepted through a trusted PROXY protocol path with a loopback bound listener.
Sources
Last reviewed: 19 October 2026.
