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/oneboxhandler.rb resolves Chat::Thread by route threadid 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.
{
"severity": "Medium",
"cpes": [
"cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*"
]
}