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CVE-2026-45318 open-webui CVE debrief

Open WebUI versions prior to 0.9.3 contain a regression of a previously patched cross-site scripting (XSS) vulnerability. The issue stems from the same root cause as CVE-2026-44549: output from XLSX.utils.sheet_to_html() is rendered via Svelte's {@html} directive without DOMPurify sanitization. This regression was reintroduced sometime after v0.8.0, allowing an attacker with authenticated access to upload a malicious Excel file that executes arbitrary JavaScript when previewed. The vulnerability requires user interaction (victim must preview the crafted file) and has a CVSS 3.1 score of 5.4 (Medium severity). The attack vector is network-based with low attack complexity, requiring low privileges. The scope is changed due to the {@html} directive's ability to affect the application's security context.

Vendor
open-webui
Product
Unknown
CVSS
MEDIUM 5.4
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-15
Original CVE updated
2026-05-18
Advisory published
2026-05-15
Advisory updated
2026-05-18

Who should care

Organizations running self-hosted Open WebUI instances for offline AI operations, particularly those enabling file upload and preview features for multiple users. Security teams monitoring for XSS in modern JavaScript frameworks, especially Svelte applications using {@html} directives. Developers maintaining Open WebUI forks or custom deployments.

Technical summary

The vulnerability exists in Open WebUI's Excel file preview functionality. The application uses the xlsx library's sheet_to_html() method to convert spreadsheet content to HTML, then renders this output directly using Svelte's {@html} directive without passing through DOMPurify. This allows embedded JavaScript in crafted XLSX files to execute in the victim's browser. The regression occurred after v0.8.0, suggesting a code change reverted or bypassed the original fix for CVE-2026-44549. The attack requires an authenticated user to upload a malicious file and a victim to preview it.

Defensive priority

medium

Recommended defensive actions

  • Upgrade Open WebUI to version 0.9.3 or later to remediate this vulnerability
  • Review Excel file upload and preview functionality for additional sanitization gaps
  • Monitor for any custom patches or forks that may have reintroduced similar patterns
  • Audit application logs for suspicious Excel file uploads or preview access patterns prior to patching
  • Consider implementing Content Security Policy (CSP) headers as a defense-in-depth measure for the preview component

Evidence notes

NVD analyzed status confirms technical details. GitHub Security Advisory GHSA-hcwp-82g6-8wxc provides vendor confirmation, exploit details, and mitigation guidance. CWE-79 (Improper Neutralization of Input During Web Page Generation) is the identified weakness. The CPE configuration indicates all versions prior to 0.9.3 are affected.

Official resources

2026-05-15