CVE-2025-54411: Discourse welcome banner user name XSS

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-08-19 · updated 2026-06-17
Weakness: CWE-79

Description

Discourse is an open-source discussion platform. Welcome banner user name string for logged in users can be vulnerable to XSS attacks, which affect the user themselves or an admin impersonating them. Admins can temporarily alter the welcome_banner.header.logged_in_members site text to remove the preferred_display_name placeholder, or not impersonate any users for the time being. This vulnerability is fixed in 3.5.0.beta8.

Affected products

discourse: before 3.5.0; 3.5.0-beta1, 3.5.0-beta2, 3.5.0-beta3, 3.5.0-beta4, 3.5.0-beta5, 3.5.0-beta6 (+1) — fixed in 3.5.0

How to fix

Upgrade to a fixed version: discourse 3.5.0. Check the vendor advisory for mitigations.

References

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