CVE-2026-91119: Discourse

Medium severity, CVSS 6.4. EPSS: 0.2% chance of exploitation in the next 30 days.

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the topic small-action and nested-activity-log components interpolated the free-form action_code_who value into mention-link href attributes without URL encoding. A quote-bearing display name could terminate the intended URL attribute and inject attacker-controlled elements into the trusted rendered markup. Although the visible mention text was escaped, the unencoded path component allowed stored HTML injection when another user viewed the affected topic action or activity log. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

Affected products

• Discourse Discourse: before 2026.8.0 (fixed in 2026.8.0); from 2026.7.0-latest, before 2026.7.2 (fixed in 2026.7.2); from 2026.6.0-latest, before 2026.6.3 (fixed in 2026.6.3); from 2026.1.0-latest, before 2026.1.8 (fixed in 2026.1.8)

Published 2026-09-24. Last modified 2026-09-28.