Open WebUI’s Banner component contains a stored cross‑site scripting flaw caused by executing DOMPurify before the marked library. An attacker with administrator privileges can inject malicious JavaScript into the global banner, which is rendered for all users, including the Super Admin. This enables the attacker to steal the Super Admin’s session token and gain full control of the system.

The vulnerability affects the self‑hosted Open WebUI platform version prior to 0.8.0. Users must verify the installed version and plan an upgrade if they are running an earlier release.

The vulnerability has a CVSS score of 8.1. EPSS is not available and the issue is not listed in the CISA KEV catalog. Because the attack requires an authenticated administrator role, the likelihood of exploitation depends on whether an attacker has already compromised an administrator account. Once the banner payload is stored, all users will see the malicious script, allowing session hijacking of the Super Admin.