A crafted XLSX file can be uploaded to Open WebUI and previewed using the sheetjs library. The library converts the sheet contents into HTML via sheet_to_html without sanitizing user‑supplied data. The resulting HTML is then injected into the page via the @html directive, allowing an attacker to embed executable JavaScript. The attacker can run arbitrary code in the context of the user’s browser, potentially stealing session cookies, defacing the interface, or carrying out further malicious actions within the user’s session.

All installations of Open WebUI version 0.7.x and below, i.e., before the 0.8.0 release, are affected.

The CVSS score of 7.3 classifies this as a High‑severity vulnerability. No EPSS data is available and the vulnerability is not currently listed in CISA’s KEV catalog. The exploit requires that a user view an attachment preview; the payload can be delivered by an attacker who controls the XLSX file. Given the straightforward attack path and the high impact of the stored XSS, organisations should treat this as a priority for remediation.