What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-10 · updated 2026-09-08
• Weakness: CWE-639

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.

Affected products

• discourse: before 2026.1.6; from 2026.5.0-latest, < 2026.5.2; from 2026.6.0-latest, < 2026.6.1; from 2026.7.0-latest, < 2026.7.0

References

• 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
• 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/security/advisories/GHSA-8g98-fvfc-9w48

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