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CVE-2026-44786 – Unauthenticated Real-Time Chat Message Disclosure – Discourse 2026.1.x / 2026.3….

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Summary

CVE-2026-44786 is a high-severity information disclosure vulnerability in Discourse, a widely-deployed open-source community discussion and forum platform. The flaw stems from missing permission scoping on MessageBus broadcasts for public category chat channels, allowing any unauthenticated MessageBus subscriber — including users who do not have the Discourse chat feature enabled — to receive real-time chat message payloads. With a CVSS v3.1 base score of 7.5 (High), the vulnerability affects multiple Discourse release tracks and patches are available from the vendor.

Technical details

  • Root cause: Chat events for public category channels are published to MessageBus without scoping delivery to users who hold chat access permissions. The everyone group assignment was not remapped to exclude anonymous users, meaning the permission boundary between chat-enabled and non-chat users was not enforced at the broadcast layer.
  • Trigger conditions: Any party that can subscribe to MessageBus — regardless of whether they have chat enabled or are authenticated — can passively receive live chat message payloads originating from public category channels without any additional action required.
  • Attack vector: Fully network-based with no authentication, no special privileges, and no user interaction required (CVSS:3.1/AV:N/AC:L/PR:N/UI:N).
  • Impact: High confidentiality impact. Real-time chat message content from public category channels is exposed to unauthorized subscribers, including unauthenticated users. In Discourse deployments where "public" channels are intended only for logged-in community members, this constitutes a genuine breach of expected access controls.

Affected software

  • Discourse 2026.1.0-latest through 2026.1.3 (all versions before 2026.1.4)
  • Discourse 2026.3.0-latest (all versions before 2026.3.1)
  • Discourse 2026.4.0-latest (all versions before 2026.4.1)

Severity

CVSS v3.1 Base Score: 7.5 (High)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Upgrade to one of the patched releases — 2026.1.4, 2026.3.1, 2026.4.1, or 2026.5.0-latest.1. The fix scopes public-channel MessageBus broadcasts to chat_allowed_groups, remapping the everyone group to trust_level_0 to exclude anonymous and non-chat users.
  • If immediate patching is not feasible:
    • Restrict the chat_allowed_groups site setting to explicitly logged-in groups only by removing the everyone group from the configuration.
    • Disable the Discourse chat plugin entirely until the patch can be applied.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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