CVE-2026-109300
MEDIUM 5.1Open WebUI from 0.6.31 before 0.11.4 contains a stored cross-site scripting vulnerability in its Markdown renderer, which treats user-authored tool-call details blocks as tool output and mounts 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.
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.2%chance of exploitation in 30 days · 12th percentile
Impact if exploited
5.1CVSS 4.0 · MEDIUM
- ConfidentialityLow
- IntegrityLow
- AvailabilityNone
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ⚠Privileges: Requires a low-privilege account
- ⚠User interaction: Succeeds with passive user activity
- ✓Complexity: No special conditions — reliably repeatable
- ✓Requirements: No special attack requirements
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
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Data snapshot:
Weakness (CWE)
- CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
References and research data (JSON)
All CVSS metrics
- MEDIUM 5.1 v4.0 · CNA Primary
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N - MEDIUM 4.6 v3.1 · CNA Primary
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N - MEDIUM 5.1 v4.0 · NVD Secondary
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - MEDIUM 4.6 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
References
Exploit-tagged references (not proof of a PoC)
- https://github.com/open-webui/open-webui/security/advisories/GHSA-9wj4-mcm3-ppj6 CVE record · VulnCheck · Updated 2026-10-12T16:04:58.200Z
CVE record · CISA-ADP · Updated 2026-10-13T18:09:47.634Z
NVD · CVE-2026-109300 · Updated 2026-10-15T15:55:45.630
Advisories
- https://www.vulncheck.com/advisories/open-webui-0.6.31-before-0.11.4-stored-xss-via-tool-call-embeds CVE record · VulnCheck · Updated 2026-10-12T16:04:58.200Z
NVD · CVE-2026-109300 · Updated 2026-10-15T15:55:45.630 - https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-97602 EUVD · EUVD-2026-97602