CVE-2026-109300 open-webui CVE debrief

Who should care

Defenders responsible for Open WebUI deployments should assess exposure and prioritize patching to prevent potential phishing or session hijacking attacks. They should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance, and plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Why it matters

CVE-2026-109300 is a stored XSS vulnerability in Open WebUI that allows authenticated users to inject malicious JavaScript, potentially leading to phishing or session hijacking. Defenders should prioritize patching and monitoring for suspicious content.

• Potential phishing attacks via injected JavaScript
• Possible session hijacking if iframeSandboxAllowSameOrigin is enabled
• Need for verification of affected versions and remediation status

Technical summary

Open WebUI versions 0.6.31 to 0.11.3 treat user-authored tool-call details blocks as tool output and mount their embeds attribute in script-enabled iframes. Authenticated users can post crafted channel messages, chat messages, or citation content that runs JavaScript in viewers' browsers, enabling in-app phishing or session hijacking where iframeSandboxAllowSameOrigin is enabled. The vulnerability allows attackers to inject malicious JavaScript, potentially leading to phishing or session hijacking. Defenders should prioritize patching Open WebUI to version 0.11.4 or later, and monitor for suspicious user-authored content.

Defensive priority

Defenders should prioritize patching Open WebUI to version 0.11.4 or later, and monitor for suspicious user-authored content.

Recommended defensive actions

• Patch Open WebUI to version 0.11.4 or later
• Monitor for suspicious user-authored content
• Restrict user input in tool-call embeds
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• 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 record and source item provide details on the vulnerability, but do not specify exploitation or victim information. There is no evidence of exploitation in the wild, but defenders should verify affected versions and remediation status. The vulnerability affects Open WebUI versions 0.6.31 to 0.11.3, and defenders should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.

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.