Auth bypass in Broadcom Rabbitmq Server
CVE-2026-67420
RabbitMQ is a messaging and streaming broker. From 3.13.0 until 3.13.19, 4.0.24, 4.1.15, 4.2.10, and 4.3.5, RabbitMQ OAuth credential refresh retains revoked runtime tags. when an existing AMQP connection refreshes from an OAuth token that grants the impersonator tag to a valid same-username token that no longer grants that tag, RabbitMQ updates the OAuth backend implementation (token/scopes/expiry) but leaves the connection's runtime #user.tags unchanged. rabbitaccesscontrol:checkuserid/2 then still honors the stale impersonator tag, so the connection (including newly opened channels) can continue publishing messages with a foreign AMQP userid after that privilege should have been revoked. A fresh connection using the downgraded token correctly refuses the same publish, proving the defect is stale session state rather than the token Limited to connections that once held impersonator and successfully refresh to a downgraded same-username rabbitauthbackendoauth2 (or an equivalent refresh-capable backend that returns tags) is enabled for This issue is fixed in versions 3.13.19, 4.0.24, 4.1.15, 4.2.10, and 4.3.5.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.003 (19.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 19.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.000
Affected products
- Broadcom Rabbitmq Server
- Rabbitmq Rabbitmq-Server — versions >= 3.13.0, < 3.13.19, >= 4.0.0, < 4.0.24, >= 4.1.0, < 4.1.15
Weakness classification (CWE)
References
- https://github.com/rabbitmq/rabbitmq-server/security/advisories/GHSA-86fm-44m9-rqjx (Exploit, Mitigation, Vendor Advisory)
- https://github.com/rabbitmq/rabbitmq-server/commit/5de287d213765ca592ff5848ad2f6b9b98ee6772 (Patch)
- https://github.com/rabbitmq/rabbitmq-server/releases/tag/v4.3.5 (Release Notes)
Frequently asked questions
- What is CVE-2026-67420?
- CVE-2026-67420 is a medium-severity vulnerability in Broadcom Rabbitmq Server, classified under Missing Authorization. CVSS score: 6.5/10. Published 2026-09-25.
- How severe is CVE-2026-67420?
- Medium severity. CVSS v3 base score is 6.5 out of 10.