What’s Vulnerable › Vulnerabilities

CVE-2026-27570: Discourse Vulnerable to Stored XSS via Shared AI Conversation Onebox

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-19 · updated 2026-06-17
• Weakness: CWE-79

Description

Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, the onebox method in the SharedAiConversation model renders the conversation title directly into HTML without proper sanitization. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, tighten access by changing the `ai_bot_public_sharing_allowed_groups` site setting.

Affected products

• discourse: from 2026.1.0 before 2026.1.2; from 2026.2.0 before 2026.2.1; 2026.3.0 — fixed in 2026.1.2, 2026.2.1

How to fix

Upgrade to a fixed version: discourse 2026.1.2, 2026.2.1. Check the vendor advisory for mitigations.

References

• https://github.com/discourse/discourse/commit/43a5a60b595f0120e6adfc131f2408508fe341f1
• https://github.com/discourse/discourse/commit/c14f8f52b7999328bd9f8665f2ecfa24dadc4bf1
• https://github.com/discourse/discourse/commit/f2aafa5c7467c94fcd4ebd36785a98e77ca088cc
• https://github.com/discourse/discourse/security/advisories/GHSA-hfxw-89hw-vwmv

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