Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the video placeholder component allowed crafted HTML to cause an attribute breakout and inject an attacker-controlled event handler. An authenticated user with default trust-level posting privileges could store the crafted placeholder in a post. When another user opened the post and clicked the video play overlay, the handler could execute arbitrary JavaScript in the viewer's session. Default Content Security Policy settings block inline event handlers, but instances with CSP disabled or relaxed could allow the script to read page content and make authenticated requests as the viewer. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

Source published

24 Sep 2026 16:56:26 UTC

Source modified

24 Sep 2026 17:25:54 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

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CVSS 3.1 · 8.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N