GHSA-hp5m-24vp-vq2q CVE-2026-44556 PYSEC-2026-2734
Open WebUI's responses passthrough endpoint lacks access control authorization
- Severity
- 7.1 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.31%
- Chance of exploitation in the next 30 days. Higher than 23.46% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
0.9.0- Upgrade open-webui to this version or later
Description
Summary
The /responses endpoint in the OpenAI router accepts any authenticated user and forwards requests directly to upstream LLM providers without enforcing per-model access control. While the primary chat completion endpoint (generate_chat_completion) checks model ownership, group membership, and AccessGrants before allowing a request, the /responses proxy only validates that the user has a valid session via get_verified_user.
This allows any authenticated user — regardless of role or group assignment — to interact with any model configured on the instance by sending a POST request to /api/openai/responses with an arbitrary model ID.
Impact
As per OWASP TOP 10 LLM:
-
Model Denial of Service (OWASP LLM04): An unauthorized user can submit resource-intensive requests to expensive models (e.g., o1-pro, GPT-4o) that were explicitly restricted by the administrator. In shared deployments, this can exhaust API budgets or rate limits, causing total service disruption for all legitimate users.
-
Model Theft (OWASP LLM10): If the instance proxies access to fine-tuned or self-hosted models, unauthorized users can freely interact with them, enabling capability extraction or model distillation without authorization.
-
Access Policy Bypass: Administrators lose the ability to enforce cost-tier restrictions, team-based model assignments, or compliance boundaries through the existing access control system.
The endpoint is a raw passthrough proxy and does not resolve workspace model configurations (system prompts, knowledge bases, RAG pipelines). Therefore, workspace-specific confidential data is not directly exposed through this vector.
Affected versions
PyPI
| Package | Vulnerable | Fixed in |
|---|---|---|
| open-webui | < 0.9.0 |
0.9.0 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
open-webui PyPI → 0.9.0
- pip
pip install --upgrade "open-webui>=0.9.0"- poetry
poetry add "open-webui>=0.9.0"- uv
uv add "open-webui>=0.9.0"
Severity breakdown
CVSS 3.1 7.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- High
Weakness
CWE-284: Improper Access Control
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
How to prevent it
- Architecture and Design, Operation: Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
- Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
CWE-862: Missing Authorization
The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
How to prevent it
- Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Architecture and Design: Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor [REF-7].
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
- System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-wvm9-9g5j-623f Open WebUI: Users denied by the OAuth role policy can still sign in via token exchange | Medium | Also affects open-webui |
| GHSA-4qg5-cxx4-g927 Open WebUI: Users denied by the OAuth domain allowlist or role policy can still sign in via token exchange | Medium | Also affects open-webui |
| GHSA-jqhh-cjmq-vmv6 Open WebUI: Any authenticated user can hang the server via a cyclic chat message history | Medium | Also affects open-webui |
| GHSA-5x7x-4c3c-qf5w Open WebUI: Server-side fetches reach blocked and internal hosts via unvalidated HTTP redirect targets | Medium | Also affects open-webui |
| GHSA-3cgp-3cqx-j8w2 Open WebUI: Any authenticated user can hang the server via message deletion in a cyclic chat tree | Medium | Also affects open-webui |
| GHSA-34r3-9m95-vq73 Open WebUI: Any authenticated user can reach the Azure platform channel via server-side web fetch | High | Also affects open-webui |
| GHSA-2724-6cpj-gf3v Open WebUI: Non-admin users can delete admin-owned external knowledge connections via knowledge base deletion | High | Also affects open-webui |
| GHSA-3pf7-q2g3-wj28 Open WebUI: Any authenticated user can inject chats into another user's folder via chat completions | Medium | Also affects open-webui |
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