Open WebUI's Base Model Routing Bypasses Access Control via Model Chaining

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.6 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L

EPSS

• CVE-2026-44555: 0.30% estimated exploitation activity in the next 30 days; percentile 23.23 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Base Model Routing Bypasses Access Control via Model Chaining Affected Component Model chaining via basemodelid: - backend/openwebui/routers/models.py (lines 170-214, createnewmodel) - backend/openwebui/routers/models.py (lines 254-308, importmodels) - backend/openwebui/main.py (lines 1696-1711, base model resolution in chat completion) - backend/openwebui/routers/openai.py (lines 1032-1037, base model payload rewrite) - backend/openwebui/routers/ollama.py (lines 1086-1090, base model payload rewrite) - backend/openwebui/utils/models.py (line 380, checkmodelaccess — checks user-facing model only) Affected Versions Current main branch (commit 6fdd19bf1) and likely all versions with the model chaining (basemodelid) feature. Description Open WebUI supports model composition via basemodelid: a user-defined model (e.g., "Cheap Assistant") can reference an existing base model (e.g., "gpt-4-turbo-restricted") that provides the actual inference capability. When a user queries the composed…

Published by the source

8 May 2026, 19:45 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-9vvh-qmjx-p4q8

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-9vvh-qmjx-p4q8

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# Patch Next advisory brief: CVE-2026-44555

Advisory: Open WebUI's Base Model Routing Bypasses Access Control via Model Chaining
IDs: CVE-2026-44555, GHSA-9vvh-qmjx-p4q8
Record: https://patchnext.com/advisories/cve-2026-44555 (revision 2, source checked 26 Oct 2026, 13:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: open-webui 0.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI open-webui: affected <= 0.8.12; fixed in 0.9.0

## Suggested inspection (read-only)
- `python -m pip show open-webui`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on open-webui.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-9vvh-qmjx-p4q8 (OSV record GHSA-9vvh-qmjx-p4q8 lists affected ranges: PyPI open-webui >=0 <0.9.0 (fixed))
- Verified: https://github.com/advisories/GHSA-9vvh-qmjx-p4q8 (GitHub-reviewed advisory GHSA-9vvh-qmjx-p4q8 lists affected ranges: PyPI open-webui >=0 <=0.8.12)

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