CVE-2026-109290 open-webui CVE debrief

Who should care

Defenders responsible for Open WebUI instances, particularly those using versions 0.11.1 through 0.11.3, should assess exposure and prioritize remediation. System administrators and security teams should verify and upgrade to version 0.11.4 or later, restrict DOCX upload and preview functionality, and monitor for suspicious activity.

Why it matters

CVE-2026-109290 is a stored XSS vulnerability in Open WebUI versions 0.11.1 through 0.11.3 that allows authenticated users to execute script and steal administrator session tokens via DOCX preview. Defenders should prioritize verification, upgrading, and monitoring to prevent instance takeover.

• Session token theft and potential instance takeover
• Execution of script by authenticated users
• Stealing of administrator's session token from local storage
• Verification of Open WebUI version and DOCX preview functionality

Technical summary

The Open WebUI application, versions 0.11.1 through 0.11.3, contains a stored cross-site scripting (XSS) vulnerability in the DOCX preview feature. An authenticated user can upload a malicious DOCX file containing an OOXML altChunk HTML part or script-scheme hyperlink. When an administrator previews the file, the embedded script can execute and steal the administrator's session token from local storage, potentially allowing the attacker to take over the instance.

Defensive priority

Defenders should prioritize verifying and upgrading to Open WebUI version 0.11.4 or later, restricting DOCX upload and preview functionality, and monitoring for suspicious user activity and session token theft.

Recommended defensive actions

• Verify and upgrade to Open WebUI version 0.11.4 or later
• Restrict DOCX upload and preview functionality to trusted users
• Monitor for suspicious user activity and session token theft
• Implement additional security measures to prevent instance takeover
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE Program record and NVD vulnerability detail provide official information on the vulnerability. The source item and supplemental sources offer additional context and advisories. Evidence is limited to public sources and may not reflect the full scope or impact of the vulnerability. Defenders should verify Open WebUI version, assess exposure, and monitor for suspicious activity related to DOCX preview and user uploads.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.