CVE-2026-45315: Open WebUI: Stored XSS via attacker-controlled file extension in /api/v1/audio/transcriptions

Severity: high (CVSS 8.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-15 · updated 2026-06-17
Weakness: CWE-79

Description

Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.3, the audio transcription upload endpoint takes the file extension from the user-supplied filename and saves the file under CACHE_DIR/audio/transcriptions/.. The /cache/{path} route serves these files via FileResponse, which sets Content-Type from the on-disk extension and emits no Content-Disposition. A verified user with the default-on chat.stt permission can upload a polyglot WAV+HTML file named pwn.html and trick any other user into opening the resulting URL — the response comes back as text/html and any embedded <script> runs in the Open WebUI origin. This vulnerability is fixed in 0.9.3.

Affected products

open-webui: before 0.9.3 — fixed in 0.9.3

How to fix

Upgrade to a fixed version: open-webui 0.9.3. Check the vendor advisory for mitigations.

References

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